340 Not firing on all cylinders

Guys, I know this may seem like basic trouble shooting to you but help a newbie out here please (without tearing me down preferably! :D )

Started the Dart up on the weekend for the first time since the winter and noticed it just didn't sound right (Didn't sound the greatest when I put it away in the fall to be honest!). So I took my infra red temp guage and took some readings at the manifold. Atleast one cylinder is definitely not firing (The readings on the left side back 2 cylinders were much colder but the back left was considerably colder than the rest).

I swapped in a new plug, no change.
I swapped a wire, no change

I did not swap the position on the distributor.

So, where would you guys head next? would you suspect the Cap/rotor or the ignition module? Any way to rule one out? I don't have a compression tester and to be honest I am dreading the thought that it is NOT ignition related!!

Also, just to be certain the plugs are wired correctly does anyone have the layout for a 1970 340. I assume the PO has them in right order but you just never know....

Thanks in advance,
Dennis