TL;DR - For what you are doing, I would buy one on FB or CL and then resell it for the same or more when done. I find that people often don't clean stuff up before listing it and it brings less money than something that was cleaned up. Although there are differences, for a short time use, I would look for one that is capable of going high enough to get the motor in and out without fighting it.
I've owned several over the years, folding, fixed, and removable legs. The folding ones tend to lack height. The mast is usually only about 4' high, which may be fine for you, but if you have to lift something high, it can be a limitation. The reach when fully extended is another consideration. The fixed ones usually have the tallest and longest reach. I doubt you will actually need 2T of lifting power, but extended you only get about 1/4 of that, so if you have to reach a ways, it's good to start high.
Also, note that the 2T rating is a bit misleading. If you put 4000# on one, it is likely to fail. Either the boom will bend, a caster will break, causing the whole thing to tip and drop and bend a leg, or some other combination of catastrophic events. My fixed one died when one of the casters broke. I had made them fixed so that it would steer decent. But when loaded with about 2500#, even not extended, one of the casters broke and the whole load came down. I was smart and was moving it only a couple inches off the ground, but it still made a mess of the leg with the broken caster. It became scrap for other projects at that point.
The casters are typically a thin web casting. Compare these, which ideally would have 4k distributed evenly, so 1k per caster, to legit casters on real caster supply sites and you'll see they are sorely over-rated.
The truss over the top often has the post forward of where the ram is pushing on the bottom of the boom. Poor design as the idea is to keep the thing from buckling.
My engine hoist with removable legs did not have the truss but was still rated for 2T. While lifting a 3500# lathe at the 2T position, it bent the boom. The other area to look for if buying is the thickness of the tubing. My Harbor Freight folding engine hoist has much thinner tubing than the one with the removable legs. The orange one that broke with the caster also had relatively thin tubing. Fixed vs swivel casters is another difference. As stated, I like the fixed casters because they go the direction they are pointed. When loaded, swivel casters often will go whichever way you least want them to go. OTOH, if you need to be able to move the load laterally, the swivels can be rotated by hand to point the right direction before pushing.
If you can find one with a double acting pump on the ram, that will make lifting twice as fast, but I'd guess most you find on FB or CL won't have that.
Somebody will say you should not move the engine hoist with a load on it. I guess those people alternate between lifting the engine/****** a little, pushing the car rearward, lifting, pushing, lifting... I'm not sure how they do it when they have the front suspension out of the car.
