I was already headed in that direction. I was looking at options from the Bonneville Shop. They have a straight 1/4 turn petcock set intended for Triumph at a reasonable price. That particular petcock requires a sealing washer for BSA application.
Straight/ 90 Degree does it really matter?
On a dry-frame A65, the petcocks are so close to the rocker cover that I think you need the 90-degree fittings to allow clearance for the hose. I have the 90 degree fittings, but I run Mikunis, with an "H" arrangement in the hose, so mine is not a good example.
Yes, these petcocks have a nut that tightens against the tank, and the washers that work are the type that are rubber sandwiched inside copper.
One other issue, up to 1967 at least, A65s had larger diameter petcocks, that is, where they thread into the tank, larger than Triumph and larger than the standard aftermarket petcocks. So my bike requires adapters to bring the holes down to the standard size, which is about 1/2 inch. (Note: Petcocks are "sized" by the inner diameter, so those with a 1/2" outer diameter I believe are known as "1/4 inch".) I believe in 1968 BSA brought the holes down to the standard size, but you may want to verify this. The earlier larger petcocks are about 5/8" outer diam.
I can recommend the B.A.P type of tap as sold by the Bonneville shop and other places, these were fitted to later Triumphs and Nortons and don't leak, I think these are the ones others have mentioned above. See This Link
Don't go for the other type of 1/4 turn tap with the longer flat type lever and circlip, I have several of these fail and leak due to o ring failure the threads stripping.
Gunner, my petcocks have a flat lever and a snap ring to hold the plunger in, but they have no rubber O-rings. But I think you're right that they are the type that were fitted to later Triumphs and Nortons.