I just went through an original position fuel tank R&R on my 49 3100 and there are a few things I ran into that you may ask a supplier up front.
I purchased my new fuel tank from an individual and don't know which supplier he got it from.
My 3100 had a bottom feed fuel tap that had 1/8 pipe threads, a short 2" or 3" adapter and an on/off valve that connected to a flex line then the hard fuel line.
The new replacement tanks bottom hole came plugged off w/an M8-125 bolt. Since it was tapped with a smaller metric thread the OEM setup wouldn't work.
Luckily the new tank came w/a new sender that was also the later model top feed version. It works great w/my fuel bowl type fuel pump. I only had to adapt a 3' length of 5/16's threaded hard line and drill a new hole in the cab to route it from the top of the tank out the bottom of the cab.
So long story short, ask if the the tank's bottom feed w/adapt to the OEM hook ups. If not you'll be having to modify/fab.
Good luck
Dave
