i went from 10-14mpg on my 80 stick econo w/ OD- the 14 being highway miles at 65 mph- to 16.6 mpg in mixed highway/city w/ a 1.21 type 2100 2bbl autolite , offy c, and FI ex manifolds. everything else stock. very useful increase in power, too. The carb is dead nuts simple. The 2100 uses midrange jets, the 2150 uses metering rods. I ran it in & about, monitored manifold vacuum, then got a 8.5 economiser valve (less than half idle vac) from Holley to fine tune it. Evidently, the 2100 jets are very hard to come by, but my plugs & tail pipe look good, so finer tuning wont be an issue. you will find a throttle cable off a v8 van is longer than the 6 cable by enough (if you are running a van) to work.
If a van, youll need a manual choke, as there are serious clearance issues w/ a automatic choke housing. As it is, I dont need any choke at all to start, tho its a little balky runnin til the temp gauge lifts....mutt, happy camper....