I wasn't able to find that number at mortec, however I did find 3998993. Which is a 75cc head used on 307's and 350's since the early 70's. Perhaps that is the head you have.
you can find that type of information at http://www.mortec.com/
These should be double hump heads. They are very sought after heads.
small block
The 4 cylinder has 1 The 6 cylinder has 2
Yes.
Not on the head gaskets.
take out the cylinder head bolts
The deck is the surface to which you bolt the cylinder heads to.
In the cylinder heads.
lt1 is a 350
Number one cylinder for v8 and v6 is always the front cylinder on the head that sticks further out on the front of the engine. The heads are offset on all v6 and v8 engines.
Change the pistons, or change the cylinder heads, or mill down the cylinder heads.