Tanks guys. I think I'll stay ported with the 340 so my dizzy adjustments will be minimal. As for the 500 I have two dist. to play with. Maybe set one up for full and one for ported and make my decision from there .
When you have time, measure out what you've got. Get a light, a tach and timing tape. Check from as slow as the engine will turn 'til its stops advancing. Then decide what steps to take next.