My engine suffix code book says the HH suffix code was used on 65,66,67 corvette 327's, 68 impala 327's and 69 impala 350's. Chevy 37's block casting info of a 68 327 would match the suffix code for the 68 impala 327. Rated 250 HP and originally equipped with a powerglide trans and a 4 barrel carb.