I could be wrong since I dont mess with anything 80's and newer but I thought all 351w were 28oz balance. None the less if I am wrong and yours is 50oz it doesnt matter it will still work. As far as the slinger it shouldnt be a problem, most shops will grind them off because they dont fit well in the older blocks. For the rear seal, I personaly feel the material used is more important then 1 or 2 piece. If you goto your local auto store and buy some generic seal you get what you pay for. Buy a good quality seal and you shouldnt have a problem.