It should be possible, in 77 & 78 I believe the Regal was available with a 301 pontiac; on the other hand, if the car has a 350 Buick in it, why would you want to change it. There may be ( I'm just guessing ) so many extra parts you need to buy and fit that it would be both cheaper and easier to rebuild your Buick. If the car is already fitted with a 301 Pont of course, it is a bolt-in.
Malc
