Jim,
I went through this same issue with my 1964 Ambassador International and
careful investigation brought to light the fact they were screw studs
meaning in the '64 black tank, they were threaded into the flange. I was
able to get them out with penetrating oil and vice-grips and replaced them
with 316 1/4-20 screws of an appropriate length. It was a couple of years
ago and I think I had to re-tap the holes as I think the originals were
something smaller than 1/4-20, (possibly the uncommon by todays standards
#12 screw thread). Its a simple sound fix and cures the problem
permanently.
--
Mitch Hill - K1FH
WBCCI 21960
'64 AS Ambassador International