/6 to V8 questions

The slant six trans will not work on a V8, if you leave that small 7.25 rear in there it won't last long. Find a 8.25 or 8.75 fom an abody or have a 8.75 cut down and buy new axles, new driveshaft will need to be built too. You will need different engine mounts, I think you can get conversion ones for that car, or you could change the k-frame.

What front brakes are you running? If you swap in a V8 you will want discs up front, can use ones from a 73-76 a-body, they will bolt right in. Front sway bar and heavier torsion bars would be smart too. You don't have to do any of this stuff but your car won't handle very good if you don't, and you want it to be fun to drive! Also, by swapping the front discs you will have the larger 5 on 4 1/2 bolt pattern, same on rear if you swap in a 8.25. If you buy new axles for an 8.75 you can get new axles with the same bolt pattern, this will allow you to run several different styles of wheels, including 15" I assume you currently have the small bolt pattern lugs?

Also need to get a bigger radiator, be sure to get a nice set of headers too. I think you could have a 360 built for a decent price, probably alot cheaper than a crate engine. No need to ditch the car, that thing looks great! I think for $5000 you could do everything you want if you take your time and do the work yourself.