If the head gaskets were copper sheet-type, they could be reused and also stacked double. You have to spray them with sealant or they will leak water for sure.
Double gaskets will reduce compression - not what you want for a race engine. The correct solution is to clearance cut the pistons. This all takes work. You need to assemble the engine with a little modeling clay on one piston top and crank the engine 2 revolutions. Cut the clay and see how much clearance you have. Depending on the engine 0.080 inch to the intake and 0.100 to the exhaust is about the minimum for a 2-valve engine. The you re-assemble and check it again.
This is one reason why pistons have an install direction! The offset pin, as posted earlier, is another.
Why is this a problem, did he intall a bigger camshaft?
It sounds like this thing isn’t likely to run at all let alone better than factory.