I've never been one to go forward with a purchase like that with the thought that I will get the rest of the parts later on to finish the expensive project. What I've always found happens is I get half of the parts and then get sidetracked and end up selling them for less than I paid for them in the first place, and walla, I've lost money and never built what I was trying to build.

I'd say back off, save your money and put something together (an engine) for the most part at once. You don't have to do everything at once of course, but at least try to get it drivable at once, otherwise you're likely to just have a $1000.00 paperweight that you auction off for $500.00 in a year.