I was wondering if any one could help me with these #'s and tell me if i got ripped off. Heres the story i bought a whats suposed to be a 79 long block remanufactured but some of the numbers are not the same. And someone said if i didnt have the same heads my motor wont run right. Heres the head numbers 3998993, GM41, D 11 3, the second one is 3973487, GM15, O 8 1, the second 3 in the 3973487 might be an 8 the casting wasnt that grate. The numbers on the engine are 3970010, GM20, H21 5 9, 010 020, The vin number by the cylinder has been machined off.
So is any of this stuff any good because it cost me 760 bucks last year and im about ready to put it back togeather and in my car.
Thanks for any help you can give.

Well, it will run, but how weel with two different heads..???? The 993 head came on a 350, but came stock with 1.72 valves so unless someone has machined them and put bigger valves, you are sufficating that side. The 487 head is a large chamber with 1.94 or 2.02 valves and flowed decent. If you want that motor to run good and ar really interested in performance, I would try to find a match for either/or. I hear a lot of good things from the 993's with bigger valves, but maybe some experts out here will give you better advice.

The 993's and 487's are basically the same heads. Just depends on the valve size in the heads. I have a set of 993's in my garage that are 1.94/ 1.50's from the factory. There is a couple versions of both heads and if you notice the design on the end of the heads you'll see that are the same for the 993's and 487's.