What's the best way to find a dead cylinder?

I bought a "supposedly" good used engine (V-8) for my truck (bad rod knock). Set it on the ground, put oil & filter in it. Installed oil pressure gauge, pulled distributer and installed a pump drive shaft, oil pressure at about 35 lbs. Pulled plugs, rigged up starter, cranked engine over. oil pressure good but took a 10 lb drop every revolution, then came back up. Compression good on 6 cylinders. # 1 & 3 zero. Leakdown showed exhaust valves. Pulled valve cover found two stuck valves, and bent pushrods. Engine not going in as is.
Actually decided to tear down. Most bearings had copper showing, Two pistons had broken rings. # 1 & 3 exhaust valves were bent, and seized in their guides. Didn't like the looks of the crank or wear pattern on the cam, so crank kit, cam and lifter kit with timing set, hone and rering. Valve job, and resize guides.
You can tell a lot about an engine out of the vehicle, without even starting it. So, check your spare engine to see if it is worth installing.