What size is the factory exhaust (head pipes) on a 69 Swinger 340-4 speed.

iirc the manifold outlets are ~ 2&5/16"

Factory should be 2.25".

Factory original headpipes are 2.25" O.D. except for the left flange pipe section which is 2". This downsize is for torsion bar , starter and pitman arm clearance.

Factory tail pipes are 1-3/4" for both 340 and 383, I used NOS ones on reproduction mufflers and had to use reducers as I know of no reproduction that are correct.

Factory tailpipes for 1969 models were 2.25" O.D. at the muffler , 2" O.D. mid of the gas tank (welded connection) and sized to 1-7/8 I.D. at the rear to accept chrome tips. 1968 models were 2" O.D. at the muffler and 1-7/8 l.D. at the rear to accept chrome tips.
Applications included both 340 and 383 engines. 1967 383 models had 2" O.D. tailpipes with turn downs at the rear as chrome tips were not an option. And yes there are reproduction tailpipes available that appear as original. Accurateltd.com. We sell a lot of them.

I will check my NOS tail pipes this week. I bought a complete system from you EXCEPT for the tail pipes because I had the NOS pair and they would not fit the mufflers you provided. I recall measuring them then and had to get two reducers to the back of the muffler to the tail pipe. I know 67's are different but these had the factory part number tags on them for 1969. Of course this was 20 years ago and you were not reproducing the tail pipes then if I recall correctly.