[jreuter]

1073 has used a similar approach for several years, using an 6WD with 8020 chassis. Yes, we occasionally need to retension the chains when the blocks slip, but this is typically only once per competition. We use 35 chain, and have not had any breakages.

The only difference I see is that we use non-rotating axles, with bearings pressed into the wheel hubs, rather than rotating axles. Our shaft support blocks are home made, but like yours have two bolts to hold them down to the 8020. You do need to pay attention to making sure the axles are not at an angle, but a combination square works OK for us.

As a possible improvement, consider mounting a flat plate in front of the mounting blocks, using more 8020 inserts. Now you will have 4-5 bolts holding the block in place, not just 2. It's not as good as a through-hole mount, but is worth a try.