At least you've got it sorted out now.
It's interesting the interaction though as you tried to inform them initially as shown in the letter, but still there was room for a different interpretation there. It seems they are certainly capable of doing this work, which is a valuable asset for quite a few of the bikes on here. But obviously need more concise details as Trigger says.
It's something that appears in other threads though. Take Laverda's 250 single piston saga as another. The engineering supply insisting that the stated clearance is far too tight (wrongly in that case) and pushing the finished result in an unacceptable direction.
It seems common that people approaching these engines just don't really take in how very concise the tolerancing is, or just don't believe it.
It's amusing that the attributes of the first 750 are usually given as "four cylinder, disc brake, ohc, electric start" etc missing completely the real engineering attributes of exemplary production tolerancing that bike brought to markets worldwide, and ultimately underpins their subsequent domination of bike sales.
That of course began in bikes like the 450 and smaller twins.
They didn't get it then and some still don't get it now, which is why most bike manufacturing went to Japan
