i put a c6 in mine about 5 years ago. Used the existing crossmember, just moved it back a few inches and drilled new holes into the floorboard. I cut and welded the trans mount to match the new dimensions of the c6. I needed a new converter, flywheel, starter and had to make some minor adjustments to the e-brake placement.
I got the flywheel from Advance using a 67 f150 as a reference.
Very easy to convert.