No way I would dive that beauty seriously ( a try in the pool maybe), I wouldn't expect any special experience from diving it. It's a BA, basta!
So even with a bigger exhaust valve I wouldn't expect a different feeling.
I'm with Kupu.
To me that BA ( a true '156') is simply too rare and special to waste it, even when I understand other opinions.
Regs are there for diving, but that one is history and in it's condition almost nowhere to find.
I would keep it for my collection, make pics for my documentation, or sell it to a true collector.
BTW Kupu, maybe that would be an opportunity for me to get even with you for the GSD Pioneer 1st you sent me for free a while ago.
I have a BA of the last generation, which is well used, but with a nice front plate you might have from another BA it could be a nice usable 2nd.
I had already my fun with it servicing it and making pics and I will definitely never dive it, so it would be ready for someone 'in need'. PM me if you want it.