I have built running-in stands for several engines. I have one for flathead V8s, one for toyota diesels, and another for the cummins 6at. They don't have to be fancy. I use a plastic lawn mower fuel tank, an angle iron battery tray, an electric fuel pump if needed, a mechanical oil pressure gauge threaded into the block... You get the idea. I make some quick side engine mounts and a couple bolts into the bell housing. My point is, you can get a really good idea of an engine's condition by warming it up, checking the exhaust smoke, the compression, a leak-down test (I've never done this one),the oil pressure, which is a major consideration. The flathead one was actually made of wood(I'm a cabinetmaker) and it was fine. The others have an angle iron frame on casters. I've done them with and without radiators. If you go without, just disconnect the water pump fill the cooling system and keep an eye on the heat. I recommend using a radiator since it can run much longer. Most any radiator will suffice for this test run. That's just what I do when I get a used engine I want to get familiar with before I install it. Great way to work the bugs out. I have done the other way where you do the initial firing with it all bolted in to the truck with some pretty sickening results.