Best way to inspect engine I'm looking to buy - leak down necessary? Plan to build it
 

I'm about to inspect an engine (stock 1.8L BP-miata engine) that I want to use as a base for a build-up. Do I necessarily need to do a leak down test or can I just pump air into the engine and listen for large air loses? Any other advice about checking out an engine that's out of the car? I should be able to pump air into the sparkplug hole (with an adapter of course) then spin the engine around the TDC mark and if it holds 100psi or so it's good, right? Or do I need to build a full blown leak tester? Thanks

If you're building it no need then for a leakdown test.
What you have to check for is stuff that could kill the crank and cam journals.

Yup. Just remove the plugs and make sure the crank turns smoothly by hand (there will be some variance in resistance to turning thanks to the valvetrain, but it'll be pretty regular throughout a full revolution.)

Make sure the engine is making good oil pressure when at warm idle. If it's a '95 or later, the oil pressure gauge in the dashboard is fake. (of course, I'm assuming the engine is in a car.)

Pop the valve cover and look at the cam lobes. Any galling or other sign of possible oil deprivation?

If you have a dial indicator and magnetic base, check the crank endplay.

Etc.