John Eales has an excellent reputation for building good V8 engines. The only downside of one of his build is that, depending on the specification he used, you might end up with something that is a bit too much for normal road use. Only a test drive will tell you.
I don't know if the 3.5 can be uprated to 3.9 but - do you know if John Eales used a 3.5 block or a 3.9?
I cannot comment on the block cracking. Someone who knows all about the V8 block will be along in a while to help you.
