Hey lumber. This probably won’t fit your needs but I put 02 Tahoe seats in my 41. They have 3-point belts attached to the seat. But my 41 is not original and it has an external fuel tank.
I’ve read where several bolters have welded brackets on so I’m sure you will get some advice.
Good luck!

~ Victor
1941 3/4-Ton Pickup (in process). Read about it in the DITY Gallery
1955 Grumman Kurbside "Doughboy" 235/3 on tree w/ OD
1957 3100 - moved on
1959 C4500 Short Bus "Magic Bus" - moved on
1959 G3800 1 Ton Dually "Chief" - moved on
1958 C4400 Viking "Thor" ~ moved on to fellow Bolter