I run a 16:1 Flaming River manual steering box on my Duster. Yes, it's an A-body, but it's a '74 so it's not as light as you might think. Before I lost the shock mounted rear bumper and giant front bumper in the Demon conversion it was pretty close to the same weight as my Challenger. I also run it with 275/35/18's in the front and a decent amount of + caster. It's my daily driver and the "newest" car that I own at the moment, so it gets driven and parked quite a bit.
Yes, steering below 8 or 10mph can be a little difficult. But it's not impossible. Most parking lots aren't that bad at all, just pays to "get it right the first time" when parking and make all your turns while you're still rolling. Parallel parking isn't any fun, that's for sure, and "dry steering" while stopped will wear you out, but that's something you shouldn't do anyway. Once you hit 10mph or so it's no problem at all, and at normal driving speeds it's awesome. I'm not some giant either, I'm 5'8" and weigh about 155 and have had a couple shoulder injuries due to my line of work (firefighter), although I am in decent shape and probably a little stronger than your average 155 lb dude.
I wouldn't hesitate to put manual steering on a car that doesn't get used everyday, especially if we're talking a 24:1 or 20:1 manual box. The 16:1 manual box is probably too much for most folks if we're talking about a daily or frequent driver, especially with wider front tires. My Challenger is getting converted to a 20:1 manual box when I get the chance, my Dart will stay power just because it's a numbers matching car and it's nice to have a power/auto car in case of injuries since I only have a fleet of old cars. Last time I sprained a bicep tendon in my shoulder I couldn't shift a manual transmission, and shifting was actually more painful than steering because of the type of movement needed.
275's are big.
