Make sure you know your application and the distributor is the right one for that application. Specifically in that year the 351W motors can in both standard rotation and reverse rotation. This refers to the direction in which the rotor spins, and is determined by the angle at which the gear on the bottom of the distributor is cut. This means that the two are not inter changable. I just rebuilt a 351W in a 87 Natique for a friend of mine and were about tho throw it back in the boat. I hate adjusting and having to change points so I want to put in a electronic setup. I couldn't find much for that motor (he has the reverse rotation) so I think were going to go with a Pertronix electronic conversion. This kit cost about $100 but I've seen a few on eBay http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=10076&item=2424853 821
I haven't got one and tried it out yet, but I should have one in and the boat running in a week or two. I'll try to remember to post how it works out.