Long shaft can go into an A body, but you have to do something with the shifter.
Dave Clements did a write up on it, there is an article on a forum some where. I think he goes by dc383 or something like that here.
Yes, I have a long tailshaft A833OD from a D100 pickup in my 68 Barracuda. I had to fabricate an adapter plate that bolts to the rear mount and positions the shifter forward to the stock A-body location (bigblockdart.com has a drawing for it). I also had to shortened the drive shaft about 3". On my car one of the bosses on the front mount would touch the torsion bar cross member under cornering but I nipped the edge off with a saws-all (or you could dent the cross member or it may not touch at all in your car).