Can a LongTail 833 tranny be used in an A-body??

Yes it can be done. Here's the article on how...

http://www.bigblockdart.com/techpages/abconv.shtml

Probably easier to buy a new tail housing and mainshaft and convert the 833OD over. A body 833OD mainshafts aren't that hard to find. And Passon sells the tail housings.