Emissions Mopar 318, Chevy 305 and Ford 302 all had cams with reduced lift as compared to the 350CID relatives. Low vaccum, low power, low fuel economy and poor driveability, especially when combined with an OD transmission.
I bought a 1982 Blazer with the 305 4v carb. It got 12.5 US MPG. I put an "RV" cam from TRW in. Valve lift on the intake went from 0.370" to 0.425". Exhaust went from 0.390" to 0.425". Duration at 0.050" was 214° int and 224° ex. My mileage improved to 15.8US MPG which was a big improvement. Vaccum was up a couple of inches and driveability with the OD was much better. The Camaro and Mustang high output 5.0L engines when introduced used the 350 cams. Considering they already had the 350 cams in use, I can not figure why they went to the **** cams for their "economy" engines. This 318 would likely benefit with a 360 cam. A big pain to install in a van, but well worth it. Not quite like installing a 360 but a definate benefit.