72blu...
Fwiw my 74 with 318 had the smallest radiator in it. 19" I believe. All stock factory and no shroud. It would run and idle all day with no issues ever, no matter how hot the weather was. I replaced the motor with a 360. Still basically stock and rad could not keep up. Would steadily climb driving or idling. The 318s bores are significantly smaller and I would expect the cylinder walls to be thicker as well. Combustion size generate the heat. Thinner bore walls will not dissipate the added heat as well. My2c
318 cylinder walls are not thicker, while the exterior of the block is the same a 318 is a different casting than a 360 or 340. If the bore's were thicker they'd all be bored out to 340 specs. Or at least to 4" like a 360, but that's still .090" over. But that's not the case. Just like 360 blocks can't be bored out to 340 bore specs (except for some of the 71 360's which used 340 castings). Has nothing to do with how the engine cools.
Cooling requirements are based almost entirely on power. A 19" radiator may have worked ok with a stock 318, but the 360 made more power and wasn't enough. The power, not the bore thickness, made the difference.
Now as for the electric fan issue/dilemma. All fans are non effective over around 40 mph.
The requirement for electric or conventional fans are based on the vehicles intended usage. If the majority of your driving is stop and go traffic (and mostly stop) such as we have out here in SoCal. Then electric fans are better to be used. Hot days and ideling in slow traffic the manual fans will not be sufficient. I attend car shows here and sometimes the waits turn into hours of stopping and starting. This kills many. Added bonus of an electric is it will continue to cool rad Coolant after motor is shut down.
If most of the vehicles driving is moving then standard fans work very well.
Point being made is there is no one correct answer.
Don't forget the climate you live in. I would like to have someone chime in about a manual fan that lives and drives in the desert...
Mike
Yes, either will work in the right setting. Like I said, my 318 powered Challenger has a regular mechanical fan. Doesn't even have a clutch, although it does have a shroud and it's a 26" 2 core radiator because it was originally an A/C car. Heck the A/C condenser is still blocking air flow out in front of the radiator. I've never had a problem with the car overheating, and it's been driven in the same 110* weather as my Duster. I've got over 60k miles on my Challenger, it was my everyday driver before the Duster took over, and I still drive it plenty. Nothing wrong with a mechanical fan if it works.
But electric fans get a bad rap. People buy them without regard to actual CFM flow, and hook them up to crappy thermostatic switches instead of controller modules. And the result is a bunch of guys that say "electric fans suck". Which isn't the case. Do a lousy installation of cheap electric fans, or even expensive electric fans that don't flow enough CFM for the application, and the result will be an inadequate cooling system. But that's not the fault of the electric fan, that's the fault of the guy that did the lousy installation.
I'd just rather see folks actually troubleshoot the issue instead of going "well I'd better put a mechanical fan back on", especially when that might not solve the problem.
Blu...I think the Contour fan is '95-2000 on the model years 
V6 model
It sure fits that core well and it seems I need to go to 26" after installing a 526. Last year at a 105 degs, I had no trouble cooling a 440 with with a smaller two row crossflow with a factory hd fan and a hd clutch. Hardly ever topped 195 degs but, I don't see much traffic in this part of west Texas
Between the over-bore and aluminum heads which tend to transfer heat to the coolant faster, I am seeing 200-205 and we have not had the normal hot days yet. The Contour fan appears to have a decent shroud included which eliminates to go find a shroud for a 26" core. Means an alternator upgrade is in my future tho as it seems both fans running will pull about 20 amps each after kick on has passed.
And as I found dimensions on the fan that says the shroud is a tad over 24", I am guessing that is a 24" wide core....I was going to buy a three pass radiator from Eastwood as I have a big three pass on one of my Buicks and it has worked really well with a front mount intercooler...but the widest one they have may be less wide than I want...so goes the mod business 
You're correct, it's 95-2000 and only the V6 Contour's and Mystique's. That's what happens when I try to do stuff from memory instead of looking it up.
I run my contour set up with a TuffStuff 100 amp alternator. I still need to do the MAD amp gauge bypass, but I've had no issues with melting anything so far. I cleaned up my bulkhead connection though and made sure everything was in good working order first. It fits the 26" wide core very well, I had to trim a tab off the top of the shroud but other than that I just bolted a couple pieces of 2" x 1/8" aluminum bar stock onto the shroud mount on the radiator to use the remaining stock mounting tabs on the contour fan.
The really nice thing about the contour fans is how affordable they are. Dorman makes a replacement, which is what is in my Duster, #620-104. $113 from Summit. Not bad for a fan set up that's capable of over 3,000 cfm on the "low" setting, while the "high" speed should be capable of over 5000 cfm. That's better than a lot of really expensive aftermarket fans, and they usually don't have shrouds included.
