Out of curiousity, what do you think constitutes "building and engine"? I would say, from what you're posting, you can put parts together. Because at some point in the past you have, and it worked. That does not mean you can truly build an engine, or that you can't, but it does say you dont know near what you think you do about it. Sorry, 'cause I dont mean to sound like an Ahole about it. But, you can buy the best parts known to man, and mess up assembling and ruin it. You need all the right parts, machined right, and the knowledge of what they need to do thier jobs together. It makes no difference if they are refurbished old stuff, or come from one source as a package. Packages are easier to buy, because you rely on the sellers opinion and judgement and experience. But when it comes down to putting it together, tosssing them together doesnt gaurantee your engine is very good or will last. So talk to your machinist. If he's good, he'll steer you right. If not, he'll make promises he won't deliver on, you'll pay too much for the results, and /or end up paying twice.
