I am (close to) speechless! How do they expect to support a large timing pulley on a bearing that's a push-fit into a piddly little 2mm G10 plate? It's shameful! Timing belts need to be tensioned to operate smoothly - any amount of tension applied to that belt is simply going to pull the pulley out of true. Any semi-competent engineer would see that!
The more I read about these products, the angrier I get! I've tried to be restrained because I realise you guys have spent serious money and I don't want to be discouraging. But there's a limit! You pay out significant amounts of money (which, in any other field, would buy you well-engineered, quality products) and all you get is a bag of bits with no instructions! When you finally figure out how to bolt it all together you find that the thing is so badly designed that there's no way it could ever perform properly. Shameful! These "manufacturers" are having a laugh - at our expense!
I've just this morning read another "tale of woe" (about a PS1 product) on another forum. These are not "isolated incidents" - this is across the board, only we don't hear about the majority (for a variety of reasons). Boris, you've documented your trials and tribulations well here - you have my full sympathy: it must be hugely frustrating.
I'm currently designing my own frame/mount and I can tell you that my "bill of materials" is about the same as what these "manufactured" items cost - partly because I'm buying all the "bits" at retail, but mostly because I'm designing it "properly". In many cases the "right" way to do something is, without doubt, more expensive. But that's no excuse for these so-called "manufacturers": they are currently grossly overcharging for what they give you, whereas what they should be doing is designing them properly and then using series production to bring their manufacturing price down, i.e. the current prices are about right for the market IMO, but what's delivered for that price is shocking!
Sorry to rant - I realise this is completely useless to you. Just had to get if off my chest!