dave h, next time you drain oil tank could you drop a light bulb in tank and report back on what, if any , plumbing is attached to the inside of your feed fitting?
is the rear mounting boxed?
dave c eluded to it----
there was shenanigans with these tanks mid 61 to mid 62.
what you have may shine light on it.
from what i can tell this is an op 61 tank.