I had a late 60's Travelall ambulance. It was 27 years ago, but my recollection is that it had a 288CI engine. (maybe it was a 266 and I'm just recalling the 6's as 8's). I also recall the engine being very similar to the larger displacement engines of the same period.
I have a distinct memory of comparing the weight of a head of the International engine with a head off a Ford 390 and the International was in a different league altogether.
I'm curious about the gas issue too. I pulled about 10 gallons of old gas out of a Travco motorhome and decided the easiest way to get rid of it was to let it slowly evaporate. Got rid of only about 5 gallons that way.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13