As you've changed a lot of things its harder to pin down - have a look at this :

http://www.intelab.com/swem/Volvo%20Ignition%20from%20Scratch.htm#Static%20Timing

I had a similar problem after fitting new carbs, cam, head etc. In my case it was because I static timed while moving the distributor CCW instead of CW and got the timing off enough to prevent the engine firing up (not bright but its the little things that get you). It had similar results to the symptoms that you describe.

It might be worth making sure that the jets in both carbs are being pulled down enough by the choke cable - maybe the mixture just isn't rich enough?

Aidan
--
1967 131, 1969 131, 1973 Triumph GT6