LOL
1. mechanics don't know 7m's LOL
2. alot of us have been there done that
you really need to do a compression check, leak down test and block check (uses blue fluid in a bottle which you put in the radiator cap, if it changes to yellow bhg is present)
you do those 3 things... i guess you could be fairly certain it's got no bhg lol
things i suggest...
if those check out fine... start saving for a new gasket and new head bolts.... you WILL need them at some stage
and don't forget when you do the hg clean surfaces, check head for cracks warps etc, clean block... new hg, new bolts, torque to 72ft lbs/92nm
racing will only blow the hg if you detonate... other than that... the gasket can handle
if installed correctly that is