Help with my engine ID
 

I have a 1970, 1st generation Monte Carlo. My Engine ID on the block is 3999290; looking at other forums this engine is for a 72 Monte Carlo. Since the engines on these cars pretty much did not change much, is it possible that mine could have this 402 as a matching engine for that year?

Any insight would be greatly appreciated.

well the 402 should have been the optional bb in 70 along with the 454, but that 402 shouldnt be the matching number 402 since its a 72 block. im going to assume that 72 should have different heads, or pistons since it should have lower compression than the 70 402. check your head casting numbers then find the head casting numbers for a 70. if theyre the same than i would assume that its got to have lower compression pistons.

3999290 casting wasn't produced until '72 and is a 402 2 bolt main 240hp emission engine so it is not original to a '70 Monte.