did that motor have composite headgasket on it?
how sure are you of the year on that motor?

02 Ls1s typically had MLS gaskets and if you look in the valley of that motor you see a BOSS that is on the early LS1s. When installing a LS6 valley cover this needs removed. In 01+ they started using LS6 blocks in Fbodys but the Ls1s of those yrs also go the treatment of not having that boss in the valley

MS3 is a beast of a cam and can be made to make great power and have good drivability.

also a blue 68 is a sick truck...one day i hope to have one