help with numbers on 4.1

[malibuick231]

I have a 4.1 block with the numbers 255429 or 2551429 on the drivers side of the block. It only has eight holes for the head bolts and the lifter valley is open like a 84 85 block. Could this be a stage one block or do I have a production block.Also it came with M and A 14 bolt heads with 27875 and 23291 stamped on the end of the heads and on the bottom it says M and A stage 3.Should I sale these heads and get a smaller set of champion heads or use these.I am only looking for around 500hp.Thanks for any help.

 

[sixgun86gn]

Sounds like a production block to me.Should hold up fine.