You can go allot of directions with that car but the first thing I'd do is evaluate what you have to start with and make a plan that you can follow. "cloning" a Barracuda into a 'Cuda is not NEARLY as simple (or cheap) as many people think, those of you who have done it know this, those of you who haven't tend to oversimplify the process. Yes, there are ways to install a performance engine into a Barracuda on a tight budget, but if you plan to do a true clone, i.e. add ALL of the correct Cuda items and upgrade the drive train & suspension to Cuda specs (regardless of engine chosen) you will be looking at a pretty expensive build. Add to that any optional equipment ( 440+6 or Hemi drive train,Shaker hood, rubber bumpers, painted or chrome sport mirrors, spoilers/wings, am/fm stereo's, rim blow steering wheels, 6 way seats, 15 x7 wheels, Ralley Dash instruments, etc.) the price can go WAY up FAST!
So, here are the front suspension basics:
Your 6 cylinder suspension is capable of supporting any engine built, the ONLY real difference is the torsion bars which are a smaller diameter,(.86" dia.) and they will work, but it would be better to upgrade them to Hemi size (.92' dia) the larger ones are only a couple hundred dollars brand new. The front sway bar would be the next addition if it lacks it, not required but prefered, all 1970-74 bars were the same on E-body cars.
The K-member is unique to 6 cylinder and for other clearance issues (besides installing the engine itself) I'd reccomend changing to a V-8 K-member (any 1970-1974 E-body V8 car has the right one, only Hemi is unique, Hemi K-members are the same but have different motor mount bosses welded to them, they are available in reproduction complete, or you can use the Shumaker motor mount adapters to install a Hemi onto a standard V8 K-member. So, in short, choose an engine, choose a K-member, choose a torsion bar diameter, rebuild suspension to stock specs. That's the basics.
Rear end:
You likely have a small rear end with the 6 cyl. engine, you could have an 83/4" which will work with any engine you install, (An even stronger rear would be the Dana 60 but they will cost allot more) The easiest way to spot an 83/4 is to look at it from the rear of the car, if the rear of the center section is smooth and has no visible bolts, it's likely an 83/4, the smaller rear has visible bolts on the rear cover and is WAY too weak to hold up to any type of performance engine.
Transmission:
You'll need a matching trasnmission to go with your engine of choice, 4 speed swaps can be expensive (figure $2,500.00 complete) but they are more popular than automatics come selling time so it's not a bad investment. A step up would be a Kielser 5 speed, but then the price doubles as well.
Radiators:
Most large engine option cars came with Max Cooling packages and 26.00 wide radiators. Your car may only have a 22.00" wide radiator and corresponding radiator opening, this is a change requiring some body work if needed, you'll need to remove parts of the opening and replace it with an aftermarket panel to widen it.
Drive shaft:
You'll need a new one
Brakes:
You likely have tiney little drum brakes all around, I'd seriously consider an upgrade to front discs, there are many aftermarket kits available.
Electrical:
Most engines required different underhood wire harnesses and battery cables, you'll likely need a new stuff as well as all the appropriate belts and hoses for you new engine of choice.
Trim:
Cuda's had some unique body and interior trim, rear tail panel stainless surround trim, rocker molding trim, emblems, etc.
Shaker Hoods:
My company makes and sells parts to convert the flat hood into a Shaker hood. If you budget $2,500-$3,000 for a complete setup you'll be pretty close.
Air conditioning:
Factory 440 6 pack and Hemi cars NEVER had air conditioning, you can add it but it's a custom job. If you want an authentic clone and your car has factory air you will need to change some firewall sheetmetal to hide the fact, the dash, heater box, and most dash controls are air/non air specific as well...Lots to deal with if you want it all to look correct.
There's more to it but this should give you a Readers Digest version of what's involved, a 13K "starter car" is only the beginning.