NOW you have the story right... !
And the 350 and 500 manx frames had different size tubings.
Reynolds had a LOT of experience with welding steel tubes together.
It is noted on their website someplace during WW2 that they welded +10,000 MILES of steel tubing into aircraft frames.
Aircrews tend to note when such things go wrong.
So the tubemakers insisting that bronze welding was required for 531 managanese moly tubing probably needs to be abided by.
Oxy welding produces MUCH lower temps (than electric), important not to disturb the crystalline structure in the actual steel.
The more modern chrome-moly type tubing IS suitable for electric welding.
But we diverge, muchly, for this frame ?