If I wasn't happy with the power I could easily get from a Rover V8 (I am running a meagre 3.9 one, so my next step would be a 4.6 - but a top hat 4.6 does command a premium. But as mine is factory V8, I will stay Rover), I'd be going modern chevy LS V8, not a 1975 chrysler.
They can be picked up for not much money, especially if you go for a more conservative one rather than the top spec - the LS engines are such a leap from the old SBC (and old fords, chryslers and so fort) that a top spec one that commands a premium is often not necessary.
And remember that the heads are ALWAYS a massive limiting factor on these old design motors (inc both Chrysler & Rover V8). I have a 9.3 litre big block chevy on one project and for the same bore and stroke, by putting some proper heads on it (matched to the cam, intake & exhaust package - but they were the cheap bits), I almost doubled the horsepower. In fact, I could easily have actually doubled the horsepower for the same £, but I wanted a nice idle and gobs of torque
So by all means do it for kicks - I've done many projects just because I can (I am putting a NA Audi V8 engine in my Ultima Spyder just because I can), but be realistic about your expecations of it, if real power is what you want, I'd go in a different direction.
And remember, it's more aggro having to order spares from RockAuto & Summit, too.
And if you do do it, please post pics! Always interesting to see an off-beat project.
I have been tempted to go ls but there just out of my price range and the wiring looks a hassel
Audi v8 in a spider sounds interesting