I made this from some scrap wood/foam for my Zephyr. One is to hold it upside down, other is to hold the frame right side up. Keeping both togher close, I can roll off the body and still leave wires connected.
Jerry Reshaw made one out of PVC pipe and pipe insulation. 2 pieces cut to length you want, two 90 degree elbows and another PVC piece cut to your width. Cover this with pipe insulation. I added legs to it. Works great. If you don't glue it together, it breaks down for easy traveling. Email me and I'll send you a photo.
Another idea that works - emergency rooms have a foam "carriage" that they lay a broken arm onto prior to putting on a cast. These work great. Now you'll have to find someone that works in an ER.
A trick I was shown for LGB engines is to use the top half of the foam packaging the engine came in. Works slick. Otherwise, I picked up a foam cradle at a show years ago. I use that with the Ariso engines.
An engine cradle doesn't have to be very complicated or robust. I made one for my live steam K-27, which is in the 30 pound range, that works fine for working underneath the locomotive. Attached is a picture of the cradle sitting on the locomotive so you can see how the cradle and engine mate. The arches are shaped to fit the boiler and cab roof. Indentations in the arches are cut to avoid locomotive details. Felt pads keep from maring the paint. The cradle was made from 3/8ths inch poplar I bought at Lowe's and cost me about $5.