I just sold my 72' B-300 maxi van Royal, bought new. Had a 318 but wanted more power. Mileage was around 14. Installed a 69' 340, milage dropped to 8. Change out the Dana 4.10 gearing for a 3.55, milage went up to 10. Your right the wind is a killer. The van was a fully loaded van and would run high 15's at 89 MPH. I could bury the 120 speedometer, but it was a slow go from 90. I always wonder what if I opened up the back doors and place a bar to hold them open and took off the engine cover to allow the air to flow threw. I also used a 2.5 exhaust welded to the collector flange. It made a big difference in performance. Tune-ups were also done from the front seat.
