Small block identification

HI all new here and just bought a 1976 monte carlo coupe s
i know that the engine must of been replaced at one time
now here is my dilema the engine casting number is 3970010
and on the front tag behind the alternator i can see the 3 letters of the suffix code which are ckt (can also see 12 but nit the other numbers)
the casting number of the intake is 346249
only info i've found from those codes is that the intake is from 1976 and up
the engine could be a 350 and could come from a 1972 camaro z28
my transmission is a th350
i'm not a mechanic so i don't know if i should open the valve cover and look for the casting number (i can only open the passenger side valve cover cause we change original valve covers for chrome ones and driver side needed to use high perf silicon to seal it good)
could it be that my engine is in fact and without a doubt a 1972 z28 camaro engine or it could be something else i'm just not confident enough to decide by myself
i'd like some help on that thanks

CKT has only one use.
1972 Camaro Z28 with a turbo 400 trans 255hp 350 Vin L with a Holley carb
346249 intake is a Q jet from 1975-77 305/350/400

The only thing you can assume is a Z-28 is the block stamping....sounds like
everything else is a mishmash of stuff.

Get the head casting number and I can decode it

i got a better view of the suffix code and it is ckt

The block is therefore out of a 72 Z28 Camaro. Now, the question is it a complete
short block and heads OR is it just a block from the camaro? IF it were an original
Z/28 valve cover, for that year, it would be finned aluminum. With the wrong intake
manifold, I would guess that the valve covers were also changed. IF you were to
remove the valve cover, you would need to change gaskets.....

i have the valve covers that were on the engine my friend put new ones on it for me but i wasn't there so i couldn't look for the casting number
to my naked untrained eyes it seems that the block and heads are the same age the paint or what is left of it seems pretty much the same everywhere the valve covers aren't finned aluminum but could also be a choice by the guy ou replaced the engine the heads may not be the originals but would it mean that they had to redo the heads to fit the engine can regular 350 or 305 heads with the lifters etc... fit on a 350 lt1 from a camaro