IIRC one of the problem children was the B29, which got hot enough for the magnesium casting to catch fire.
All of these motors had really big lifters, the stem itself would weld to the lobe.
Gravity is far too weak to be of real help, the valves open and close too fast.
They definitely need more spring, and how much spring is reduced by saving every gram you can. Too much spring adds torsional load to the cam (twists over the extreme length) which upsets the timing at # 5 and 6.
A 265" L6 (3-7/16" bore by 4-3/4" stroke)is about the size of my Harley flathead engine: 3-7/16" bore by 5" stroke for 92". I'm using 5/16" OD intake valves to both reduce weight and increase port flow, the valves are over 6" long, 2-1/16" head. The exhaust are 3/8" OD to keep a lot of contact with the guide for heat but smaller at 1-3/4" head.
The cam is dual pattern, with roller tappets.
Intake: 294° @ .010", 270° @ .050", 49-65, .377"
Exhaust: 278° @ .010", 256° @ .050", 60-38, .407"
The numbers look funny, but there isn't much available for these - not made since 1948.
