if you have built motors before go for it if not have someone else do it seen lots of motors destroyed by backyard builders my first motor someone had turned one journel down we missed it but didnt on the secound rebuild with a new crank
If you don't have a go you will never have the experience to rebuild an engine. I have rebuilt one engine and I learnt what to do as I went. I used professionals for all the machining, and they knew I was going to have a go at it, so they offered me advice and checked all the tolerances particularly well to minimise the odds of errors. Rebuild went well, learnt heaps and had a lot of fun doing it. The engine could probably have been built better, but I did it!!!
GO FOR IT!!!