I recently did this conversion on a 65 Coronet. I used a 66 K-frame, 727, and was able to use Hooker 1 7/8 headers for 66 and up B-body. No problem with trans tunnel clearance unless you try to use the 66-67 driveshaft that has the big collar weight on the front of the shaft. I was able to use the 65 trans cross member as well. I did use a B+M cable shifter and a Lokar kick down cable set up. Basically a bolt in swap. I did have to fab a mount for the shifter cable on the transmission. A piece of angle iron and a drill, took all of 15 minutes. Oh yeah, the car has power steering and no issues with clearance there either.