You also mention a K&N air filter in there. For #$%*s and giggles have you tried going back to the original air filter? Sometimes they can make things overly rich if it's excessively oiled. It may also change the air/fuel ratio which means having to experiment with jets, which may be "fun" to you but it's not to me.
For what it's worth, and I have not verified this, but I've heard plenty of anecdotal evidence from Hondaman on these forums that air leaks on these particular type of carbs used on the SOHC4's will actually cause a rich condition. If there is an air leak and this is true, then that could be the issue.
Also, keep in mind that coils can read good on a meter, but may not show a problem until they get warmed up and then the resistance changes and causes funny things to happen. You can always swap the coil from one side to the other and see if the plug colours move from 1-4 to 2-3.
Condensor is probably OK. A lot of people blame them, but they seem to be fairly reliable if the bike is stock. There's a few tests you can do, but the easiest one is to run the bike with the cover off in a dimly light area or at night and see if the points are excessively arcing. If they are you can get still get new OEM condensors or you can buy Hondaman's transitorized ignition box which bypasses the condensors, but keeps the points. This will prevent the points from wearing out further, eliminating the arcing.
Some slight decel popping is probably normal IF these carbs don't have an air cut-off valve. I don't know if they do, but if it's mid 70s then I would say probably not. Someone else will have to chime in on that because I don't know what a total stock mid-70s era 750 is supposed to sound like during decel. From what I have read on here though, it is apparently normal and that the stock exhaust was designed to hide it quite a bit.
