Be careful if you are still running the stock Y pipe. The 4 bolt setup will NOT fit the 2 bolt factory Y pipe on an Olds. You'd be better off trying to find a cat end or make something with a 2 bolt flanges. Also the down pipe has a 4 bolt connector, but is square vs. rectangular pattern.
Looking for an OE CAT as you mentioned. I currently do not have anything past the downpipe. I am eliminating headers I put on in '89 when I was 19 and going back to stock 350 manifolds, crossover and downpipe from a '79
H/O but would like to go with an '83-'84
H/O style from the CAT back. So I have a couple variables to deal with like you say to make everything fit up. Looks like I may have to go with the Hooker 16810 kit OR continue looking for an OE CAT for a '79
H/O and do the '79 single in dual out muffler as from factory. Thanks for the input, greatly appreciated.