Many modifications to the original plan. Couldn't get the engine plate to move up and down reliably horizontal. Solved the problem with some good advice from "clever friend" Dave.
The plate was originally suspended from the hoist and sited by four wheels to lock it into the side frames. I had the side wheels too close together (twelve inches apart vertically).
I added some metal and extended them to a distance of two feet. Changed the top two wheels (metal lawn mower wheels) for rotating castors to allow a bit more side movement to stop them sticking. Much more stable now. Also changed the position of the choker hook from the back of the hoist to the front, which helped with the alignment as the plate rose. Had to fabricate a new slip out safety clip on the hook as well as the old one perished almost immediately. Also added a spreader bar between the two castors. It can move front/ back (20 degrees or so) to accomodate the side to side travel of the cable as it winds up and down on the hoist.

The next job is to mount the trannie and the engine on the engine plate.
The workshop picture is of the "original" plate without the extra side bars and castors.
In the movie the brake rotors are to simulate the engine and trannie weight .
Still a little rocky on the descent but working on that now...

Fixed the horizonal problem finally! Moved the hoist hook three inches in front of the hoist.
The hoist cable was pulling the engine plate into the sides of the rails and jamming it slightly.
Now the plate rises vertically and the castors and wheels don't jam.
Also raised the hook by about a foot which gives me a bit more vertical lift as well.
Now I guess I have to do another movie of the plate rising freely. (just to show off!)