I don't much care for diamonds an anything watch related! They only belong on fingers or ear-lobes...
Sly, if you can find a suitable dial I've probably got the rest of it covered...
I have not built up a mid-size Rollie from a gen case but have built a Tudor with a rep 31mm case. The cases I have are for a 2836 and no spacer is required as the movement completely fills the case. I would suspect the same would hold true for a gen case. You just need to get the right stem location to line up with the case tube. I look forward to your finished product!
Here's my Tudor:
You will likely have to slightly countersink the tube hole in the case as you will notice the gen type tube is constructed differently than the rep tube.
The tube is supposed to stay on the hand. I put a little Rodico on the tip of the small flat tip on my hand presser so the hand will stick to it and it's then very easy to press it onto it's post.
The DG2813 I bought from cousins had a recessed pinion for the sweep hand. The 2813 I got from ofrei worked out OK. I don't know if this can be specified to Cousins or not but it might be worth an e-mail...