I have 265 wide tires, relocated perches and offset hangers. They still rub. 275 would never fit in mine (72 swinger).
I'm going to be doing a mini tub and inboard relocation to the frame rails once I finally commit to my new rear end so that I can fit 295s back there.
Even with just 265 wide, my 408 equipped car wheel hops more than it smokes! LOL. My snubber doesn't hit the floor and I'm running kit car springs which push the rear about 1/2" further back for better clearance at the front of the arches. I'm debating a custom third link or traction bars or custom leafs to fix the hop issue.
I'd also say the 4spd conversion isn't that bad. I did it in about a week with the parts in hand. Hardest part was honest swapping the u joints (had to swap yoke's since I had a 904 before). I bought an amd hump, and the sheet metal work was honestly super easy. The pedals were a lot of work, but if you've ever taken the column out, it's really no worse.