Brief update:
I once AGAIN made new side rails. Decided to try putting the tension adjusters thru the end of the beam and thread into the axel shaft on the idler tumbler. I like this design, the brackets on the outsides were difficult to the size down so they didn't look out of scale. I might have to drill a few pads with access holes to get at the adjuster screws.
I drilled and taped the drive tumbler and powered it with my drill. I still have an problem with the pads shifting to one side and then the drive and/or idle tumbler catches the drive dog on one pad as it starts or tries to enter the drive tumbler.
Today I am going to make the lower and upper rollers and see if that helps keep things lined up.
Also going to try standard pulleys and O Rings instead of sprockets. I can make them easily, they will provide a lot of "give" if something binds and I have the parts on hand. Hope to still use sprockets and chain at some point.