RE: 50cc-ish reasonable $ twin? ISO engine for 12' Tele
The DLE would be your only low cost choice. Even so there arestillplenty of problems with them which is most likely why so many people cantell you who gives good service and who doesn't.
Any of the low cost "cheap" 50 twins you mention have a long history of problems if you follow the forums and press. Expect to get one, strip it for your own peace of mind, order parts to replace the parts the factory has used when they should have been thrown out, wait for the parts and if the correct parts ever arrive, reassemble the engine and hope it stays running.
There is another long thread on this forum about twins in this size. Seems there is a lack of decent options in the size range and no decent options at a low price.
The 12' Telemaster is a nice flying plane. Why stuff it up with a cruddy engine for just a couple of bucks saving?