I'm running an `89 with the OEM wheels, and I went +2 on the rear sprocket for 17/50. The chain-length on the `89 is 112 links according to my manual, and I have no idea whether I added more links or not... I bought a 120 link chain and cut-to-fit. You might find this thread useful... there's a link to a gearing calculator there that you can play with and iron out your sprocket sizes that way.
I'm running a 15/48 combo for a 530 chain. 15/45 is stock. I needed 2 more links than a stock chain to make a nice fit (108 to a 110) with the +3 rear. Your new set-up, I don't know how many links you'll need. The stock set-up was great for freeways, the +3 is alright too.