Just picked up a 69 Cuda...

Good luck finding a cheap 6.1 not going to happen unless you get real lucky. 5.7 can be stroked to run real well. It's all about how deep your pockets are and if you have the mechanical skill to do the work yourself. If you farm a swap like that out, first you'll have to find someone who knows what's goin on and second it's going to be pricey. Sounds like your a busy dude so take your time and enjoy the build if you are going to do it. Oh yea a well prepped 340 will haul some serious *** way cheaper than a 6.1