Congrats on having a 67 GTO, I had one of those way back when (1980's). It sounds like it is pretty muck stock I am assuming. You have a lot of the typical symptoms caused in part by the fuel with alchohol these days. I would say that a rebuild would be in order. You will need a complete kit from Cliff but I would think that not too many mods will be needed if the car is stock. Sounds like the stock carb too. The most important pieces would be the new alcohol resistant accelerator pump and the needle and seat. From there I would check to see if the well plugs are leaking as the old carbs tend to leak. Check to see if the pull-off is functioning (vacuum pump handheld or just disco the vacuum line to it while idling). As far as mods, I guess it wouldn't hurt to open up the holes under the idle screws a bit and maybe one size up on the jet. Of course, check to see if the choke is functioning for warm-up purposes. I guess you should make sure that all the parts are of the same specs to the original cause it sounds like I wouldn't trust the previous rebuild and who knows what else has been done on the inside. OK, time to get to work