recently I decided to upgrade the motor in 1997 heritage classic. A friend of mind introduce me to a guy who builds race engines for car and motorcycle. He built me a 121 inch motor with all the trimmings, motor was very fast compared to my stock motor, but after 3 months it blew head gasket. I put motor in shop and first thing they told me was I had sportster heads on my heritage classic and that the heads are warp and he use silicone to make them work. When I asked him about the heads he said sportster heads would work on a evo engine. Is this true and if not why