Yer,done a bit with those motors.NGK B 7/8/9 HS as opposed to ES.
Yamaha never recognised the A suffix ;they simply called them 250 or 350 but there were subtle graffic differences on the tanks between what you and I would call the 250/350 and the 250A/350A.
The first post DS7/R5 models had a plate in the box to prevent 6th being accessed that was ommited on the A models.
You will know all this.
I ran a 250A then an R5 then XS2.
Did 500 production with a 400F then moved onto TZ350A in the late 80's.
They were the tits in their day.
Well done on putting another of the "352" series back together.

Did you manage to source the plastic plugs that go into the cap screws on the h/b mounts ?

Another way to spot an A from a B is the tank badges, earlier models had metal badges and the "original" RD did have different tank graphics and colours from the "A" model, otherwise the same thing but you have to look really close to tell.
Anyway you know the subtle differences as well, even down to "352"....................
As for the plugs for the handlebar cap screws, I found Yamaha still do them, along with most of the service parts and they are starting to remake some of the NLA parts due to demand..... they have just started supplying 250 and 400 pistons and rings again among other things.

I just remembered about the brake light indication lamp in the instrument cluster-a cracking idea that should have been retained on later models but was probably superceded by fitting 2 bulbs to the light housing.

They replaced the brake lamp check light with a 2-stroke oil level warning light.