1970 Skylark 350/TH350. Shortened the driveshaft when the 8.5 rear went in. Putting in a 200-4R in the next month or so. Is the driveshaft already the correct length?
Very close to the same length, but doing a proper measurement with suspension loaded to make sure. For no other reason that the number of years and hands a car has seen messing with its dirty bits, can leave you with an unintended "gotcha".
Mine is 55-1/2" CTC. Also depends on the shape/ profile of the yoke. Some are square like this, some are rounded a bit.
When I went from Turbo 400 and Chevy 12-bolt to a 200-4R with an 8.5 Buick, I swapped my old driveshaft for a 1971 Buick 350 turbo transmission without any issues. At full droop, it doesn't bottom in the transmission. But, verify for peace of mind.