It would be a fairly simple task to make replica mounting from steel and fit to your standard frame, welding is also a lot simpler/ easier to a steel frame, aluminium is a right pain once painted /treated , although I know of a company that doers aluminium welds for me very cheaply, I'm looking forward to the 1000w Ultra Drive being released to market, its dimensions are only 2mm different to 250/350w units.
The Max Drive is extremely popular in China but little known elsewhere, spares are available for the drive now , but only from Australia, we have to hope that Bafang Europe (NL) start making the spares and units available to all ,
I did consider making a replica for a moment, but as I have not actually seen the max drive IRL, I have no idea what sort of precision would be required.
I would think there are mating surfaces that need to be flat and parallel and correctly spaced..
I guess one could use the motor as a template. Bolt some small steel tabs to it, connect those by welding, then fill in the spaces and then try make that whole thing look non-fugly by diegrinder or something..
Another approach would be to "grip" the alu bracket in a steel bracket. That would probably have a higher chance of success by a non-pro.
I have both a MIG and an and oxy-acetylene torch in my little workshop so I could probably pull off both of those approaches, but I'd leave the actual frame welding or alu-welding to a pro.
On the other hand I'm looking for a bike, preferably before the season is too far gone, and not another escalating full time hobby
About the max drive's popularity there seems to be quite a lot of bikes based on it coming this season here in Norway. I spoke to a guy recently that apparently expected a container this week.