I'm not sure you need machine shop or vast materials knowledge to evaluate these engines. A few guys tried the GO engines around here and did not like them. I think they did get decent life out of them but the performance/fuel economy was not what they were hoping for and there were some tuning issues.
To the guy with the RB. You probably have the engine too lean on top. Normally a high idle after full throttle run means the top is too lean. The S7 does not make great bottom end and a clutch that engages too early may fool you into thinking you need to lean the engine out. There are a few other engines out there with that problem.
Ultimately you will spend far more money travelling, paying race fees, and paying for tires than you will on an engine so it is best not to skimp too much in this area. The power band and stability of tuning are most important and fuel economy can also be an important consideration.