I had this same question when I first was planning the build on my car as well and found that the price to swap the 5.7 was actually pretty comparable to several other options I was looking at. A fairly vanilla 5.7 swap, a lightweight big block, a forced induction small block, and a small block stroker were all coming up around 5-7k for me (I put together a spreadsheet with all the different part prices). When I originally did the swap I went with a carb setup and had it in the car and running for probably 5-6k all together (I didn't get a computer or harness with my engine anyway). I later came across an awesome deal on a Megasquirt 3 and have since converted back over to fuel injection.
One of the big reasons I leaned toward the newer engine is because of the potential and general advancements in engine design in the past 40 years. As many have mentioned, some very light work easily puts you into 400hp+ territory. Doing that on the older engines requires a fair amount of high end parts.
I'll be the first to say my gas mileage hasn't been what I was hoping (currently around 16-17) with a 4 speed and a 3.55 rear gear instead of the 20 that several have seen. However I also realize I pretty much doubled the horsepower of the little 318 that was in the car when I bought it and kept the same gas mileage, so that's still a win in my book. I'm sure there's probably a little left in the tune to help bump that up, but it's been running well so I haven't messed with it. My next project is a T56 swap to get the overdrive that I really want once I find the right trans.
Long story short, the 3G swap is now pretty much entirely bolt in, which was one of the main reasons I attempted it. I don't have the fab skills or tools to make my own headers and do significant sheet metal work, or I would have probably gone with an easier swap. The parts are a little more expensive than other brands (like an LS swap into an old Chevy), but to swap a plain stock 3G into an old car really isn't that hard. The main thing that seems to hang most people up is the electronics. They don't really bother me, but they are a black box for a lot of people. Unfortunately they just don't seem to have a good solution for this yet. I originally looked into the FAST EZ-EFI system. They make a kit that's designed to work with stock fuel injection, so it's essentially just a computer and a wiring harness that self tunes, but I believe you have to have GM sensors, so you might have to adapt a couple of things.
Next time you get near a modern Chrysler car with a stock Hemi, have a listen. depending on the year, you are hearing 350-400 HP. Now listen to a 400 HP LA small block. The modern hemi makes similar power with a lot less stress. Add a cam and headers and you are over 400 and it almost sounds like your mom's car.
The reasons for me are:
Less weight--I thought it was 70-80 lbs less than an LA. I'm not interested in A/C, power steering, or power brakes.
Better MPG--I actually like driving my car and if it got better mileage, I'd probably drive it even more. But....I'm convinced the key is overdrive trannies to max out the mileage no matter the engine.
Good power without the compromises of a built LA.
Smoother operation at all temperatures--It's pretty much gonna start without having to worry about chokes, flooding, washing down the cylinders with raw fuel, etc.
My quandary is my 68 is loud, smelly, creaky, hot, and I love the sound of the AFB opening up (and the gas gauge needle going down). And don't forget the sound of the classic Mopar starter.
I like all that. It's what a Barracuda should be and I look forward to it every time "I jump in and fire that mother up".
Is a 68 Barracuda still a 68 Barracuda with a modern drivetrain, sound insulation, big wattage system, leather interior, temperature control, etc.? I'd probably miss all the old stuff but I still want a 5.7 in my cuda. But that's where my 69 comes in as it will remain as close to stock as possible because of it's pedigree.
It's approaching a modern street rod built from a catalog. A fiberglass 32 Ford roadster, aftermarket frame and suspension, modern GM LS engine with A/C, satellite radio, power windows, power rack & pinion, etc. Really? Can you still call that a 32? Not a single part is 32 vintage.
Or a 62 Chevy built on an Art Carr chassis.
Or a NASCAR stock car.
