At Holinger, we also have a CMM. The measuring is the easy part. To measure the co-ordinates of just the bell housing would take half a day. It can also be done with a mill. It comes down to more than just a few things. The dowell positions of the block govern the position of the gearbox as well as the starter motor spigot. If dowell positions arent a perfect match between the new gearbox and the block then there must be sufficient clearance that they will not interfere with one another or the adaptor plate will need to be thick enough to compensate for the two sets of dowells sitting almost on top of each other. As the A series dowells are at the wide as point it makes it a bit difficult as they do interfere with L series bell housings. This can be overcome. But not with offset (eccentric) dowell pins. You need to make the adaptor thick enough to clear both pairs of dowell which brings your adaptor plate to a minimum thickness of 22mm.

So the trick is to find a bell pattern that the dowell do not interfere. Then you can achieve a 10mm plate.

I would find out how much it would cost to get your plates and housings CMM'd before starting as this would have to be calculated into the price of the adaptor.

There are more things but I don't have the time right now but good luck. If it can be done cheap I'm on board for sure, in fact I'll even see if I can con my boss into doing the CMM work for free.