I finally got a decent job (go me) and have the money to build up a frame I bought a few years ago. It's an early 90s steel frame so I'm building it up with early 90s parts, mostly from eBay. I'm now looking for a stem but I'm not really sure what length to get since I've never ridden the bike. Does it make the most sense to build it up sans stem, then get on it and try and guess an appropriate stem length, or is there a more scientific method I could use?

I was also thinking of just buying as many different length cheap stems with the same drop as possible, and seeing which one was best, then buying a nice one to actually ride with, but this is of course the least economical way.

Anyone have a good method?