I determined the length by setting fuselage level with stick and elevator bellcrank in a vertical position. Then with elevators in trail the rear pushrod length can be determined.
The forward pushrod can be removed rearwards but you must ensure the clearance holes in bulkheads F305, 306 and 307 are sized as necessary. A draw string tied on prior to removing the pushrod would probably assist in getting it back through if your seat pan is attached per plans.
I should say that I am not a "veteran" RV 3 builder but rather a first timer, and this is just how I did it...
RV 3B. Very slow build. Now onto final assembly...