I think with OD the 220 can get better mileage than the 132 because of the
better aerodynamics. ("Aerodynamics is for people who don't know how to build
engines!"-- Enzo Ferrari) I made a trip in my big bore wagon one late night in
Panama where I got about 33.3 mpg at an average speed of about 65 mph. It was
300 miles and when I filled up I was down 9 gallons. First (and maybe only)
time I ever made that trip on one tank. I had been orchid hunting in the
mountains in dry season and was going to stay with friends but the car and I
both had about half an inch of red dust on us. My friend's wife insisted on
cleaning the shower but just as she got it clean the water went off and I was
MUCH too dirty to sleep in someone else's bed so I went on home. Made it in
about 4:40. Speed limit there was 100k in some parts and 80 in others but
I didn't see any flashing lights, oxcarts or drunks passed out on the pavement.
(It happens!) Got a shower that gradually cleared from rust-colored to clear
over about 20 minutes when I got home. The car wasn't as dusty when I got home,
except inside.

I believe a 121 with 4.1 and judicious driving can probably get over 30 on
a regular basis on the road.
--
George Downs Bartlesville, Heart of the USA!