I think the biggest difference between prs and diy ers is kit the pros have grands worth of measuring kit and the knowledge to go with it, best bet if your going to do it yourself is to make friends with the local machine shop as they will have kit to do measurements for you and get as much info as poss but if your going to build a big bhp motor probably best leave it to pros as mistakes are expensive as i found out many years ago then it works out cheaper to pay somebody else