After several attempts, I have finally reached a reasonable solution for motorizing the Peco turntable. The two pictures show the arrangement:

Basically I gave up with attaching the motor directly to the plastic well and created a strong plywood substrate. The need to reinforce the plastic well now seems to be unnecessary, so those three holes in the plywood are no longer used.

Meccano parts did indeed come to the rescue. The motor is noisy but not as noisy as the previous kit and the gears run nicely with an application of lithium grease. The DCC control uses a TCS decoder and speed is easily controlled at a realistic level.

There are still several cosmetic touches to finish on the top side but these can wait while I re-jig the coal hole/water tank that will be scratch built later this year.

If I was to start over again, I would seriously consider an indexing kit