The bands I have on them now are 14" combined with the heavy wishbones from JBL, used on the bigger Magnum series guns- you'll recognize them by the flat section that fits into the notch of the shaft, red side down. You may have to tune up the notches to get them to fit smooth.
The earlier triggers, as in waaay old are fine for this use; if your gun has Swimmaster or Voit on the handle, you're golden

Later guns fell to the bean counters that figured they could scrimp in the trigger area and save a sheckle every 37th gun, so be careful to take a gander at the sear and the safety notch. The safety will let go first as you'll have to smack the thing down with a rock to get it loosened while loaded. The new ones are supposed to have heat treated guts and all, but I've taken two apart and one had beefed innards and the other didn't so take your chances. Either way the trigger pull gets a tad much so get your grip going and forget about a smooth trigger pull- it'll end up being more of a quick clutch of the trigger, but seeing as how the fish here are all so stupid and easy to shoot, (Turdgeon, 2002) it's a moot point.
You
can whip out the fine file you tuned the shaft with and
gently ease the trigger sear, but you gotta know what you're doing, otherwise you're just going to introduce an accident quick. :blackeye
Using 5/8 bands is fine for the pure
punch they can put to the shaft, but they're not the ticket for longer shots, and with the Custom or 4G32, that's 5 feet. The stretchier 9/16 rubbers would be better here as they'll actually stretch further and impart more velocity to the shaft. Since most of my shots are in caves and holes where the fish often doesn't let the shaft clear the muzzle, and I shoot the heads, the 5/8 band's punch is dakine. Much over 3 feet away and I have to do the wiley stalk, and with the red vermillion that's a job...
sven