Odds are that your new treasure has a spring ("Graphic") back. If you don't know what that is or aren't sure what you have, visit www.graflex.org and read the FAQ.
If you're willing to use it to shoot 2x3 (also known as 6x9, but Graphics are in inches) and are patient you should be able to find an Adapt-A-Roll 620 to fit a 3x4 spring back. These devices slip in like sheet film holders, must take up on a 620 spool, will feed from a 120 spool. They exist, I've had one. Sorry, sold long ago.