get the correct size grommet, grease it, and get it started at the filler tube, I used a 2x4 between the tank and the frame, put some (a bit) pressure on it and "thump" it slid in. Just make sure it's lined up good.
'67's only came with a single exhaust also, 273 Commando and 383. I got a 2.5" Pypes dual X pipe and tail pipes under my '67 though. Slightly lower but not a lot without notching the x member
if this is successful it's the first time I've been able to attach a pic.
this is the screw you will be looking for but the vent window frame has to come out to access it, it clamps down on the lower pivot pin, dont lub it.