Interior cost isn't anything compared to all the drivetrain and engine/transmission parts costs. I am rebuilding a 73 Duster right now and I wish it was the cost of an interior lol. Good luck though no matter how you proceed.
I'll have to keep that in mind. From what I've read, swapping to a 318 shouldn't be too big a deal right? I've got an engine and transmission lined up for super cheap, just have to go get it. But from what I've found so far, its pretty much just a matter of changing the K-member and getting the right motor mounts right? I probably won't worry about rebuilding the engine right now, maybe just get some new valve covers and stuff like that and clean it up a bit.