3858180 is a casting number for the 64-67 327 block and can be anywhere from 250 horsepower thru 375 horsepower....so that part is fine with the claim that it is a 65 Corvette block

Your code on the block pad (passenger side, just in front of cylinder head) doesnt make sense....there were 19 suffix codes for Corvettes in 1965: HO HQ HE HI HP HR HF HJ HT HU KC HV
HW HH HK HL HG HM HN

Note that all but one start with the letter H and are of two letters.

mike in tucson