I made one from an old air bumper jack a body shop was throwing away, I made the platform from a couple of rack body lift ends (the part you drive the vehicle up onto a rack lift which fold down when the lift goes up) that a muffler shop was tossing.
Here's a slide show, I had posted to the old list, but the post is NLA, just click the image:
I made a work table from an old steel door and some pipe, both being tossed by a plumbing supply.
No more aching back, slide the engine down onto the table, when done, lower lift and slider'er back down onto the lift.
I've seen a few of the bumper jacks for sale/free on craigslist, they're basically useless to most shops since cars don't have real bumpers anymore. I did it on the cheap, the most expensive part of the build was the paint and the channel stock, which were about the only things I had to actually part with money for. I painted it camo so it would blend in with the background and keep the wife happy (out of sight, out of mind.) Since these pic's I've added a couple of proper ramps for the ends (from synthetic "wood" left over from a deck project.) I'm really hoping the local funeral home gets a new coffin hoist, I've got dibs on it, weld that to the top of the lift cylinder and should able to either lift stuff that's on the platform up, or do a double lift, one on each side for parts transfer or dismantling. Makes a dandy stump puller too.