Shane;

Popping from the exhaust can be an ignition or mixture or valve problem...unfortunately since you've made changes to all these systems, so it's tough to make a quick diagnosis before bringing everything to a nominal starting point...it's good practice, if you're not absolutely sure of yourself, to work on, and change only one thing at a time, and then check out the effect it has (and don't take this as a comment intended to be offensive...hell, I use this technique when I can!). By making changes to one system at a time, it allows you to more easily narrow in on problems...by changing a bunch of things, I don't think anyone is able to say definately what's wrong...especially since many of the changes affect each other...

...so its divide and conquer again...

Ignition: I suggest you start by assuring the ignition is allright, including correct gap, centrifugal advance free and returning properly, timing at 16 BTC, and as far as I'm concerned s***w the dwell. Once started, verify idle timing with your timing light...since you can, might as well rev it a couple of times and check the timing advances and returns consistantly.

Valves: If the valve settings are open, they will clatter, but if they are tight, they may cause burned exhaust valves...double check to be safe. Use a necked down feeler gauge as shown in swem service notes page to get a correct and accurate setting.

Carbs: Start with jets flush with jet glans at venturi, and if metering needles have been removed, their shoulders should be flush to dashpot surface. Double check that linkages are activating the carbs equally and back of on the idle adjustment screws.

Good Hunting. Please let us know what you find.