Are you using a real Grubee frame, or the gasbike/kings knock-off's?
The real ones come in a box like this.
Gasbike.com can't buy them wholesale, haven't been able to buy anything real Skyhawk factory made for a few years now.
Are you a rep for them?
Given your handle it's hard not to think so, but I'll assume you are not ;-}
My local welding shop has no problem welding my aluminum custom plates on them, and none have cracked or broke anywhere, but I have heard the knock-offs gasbike sells have that problem.
160 discs front and rear.
Your new mounting design looks promising, pretty much anything beats the stock mounting system regardless of the maker.
4-Stoke engine kit MB's aren't near as popular as 2-stroke's because of price, but that gap is closing and the benefits of going 4-stroke becoming better known.
And then there is the many different transfer cases, most of which are junk...
I have new "Complete Motorized 4-stoke Shifting Bike Kit" coming a little later this year.
It will be a limited special order item that actually could be assembled in a weekend exactly the way you want it.
The gas tank frame with a welded on base mount with holes not slots to mount the engine perfect.
Powder coated however you like.
My 10G 4-stroke system with bottom bracket work already done.
I perfected that when a local brought me a frame, engine, and a bunch parts.
He picked a frame color, provided the front fork, etc. He just got to it local is all.
What I intend to offer is something similar to that in 3 boxes depending on what you want.
Far cheaper to ship than a completed bike, but with proper assembly you come out like you rode my custom build right out of my shop.