The 4.9L is an almost legendary 300 cubic inch engine, it is an extension of I think a 270 CID engine, dates back to the late '50s or early '60s, although the 300 version came about in the late 1960s. An actual TRUCK engine (no cars ever used these). Beastly huge thing. Low stress, low RPM, low HP, high TQ. They are virtually indestructible. They were used in a lot of step vans and stuff, too.
They are thirsty.... the later ones like mine, manual or automatic, were rated 15 cty 20 hwy, but in order to tag 20 you'd have to be moving pretty slow, like maybe 60. Otherwise, it is around 14 to 18 for me. They never were bolted to the passenger car OD automatics, either, just the big 3sp C6 or the later E4OD (which became the 4R100).
Low tech, but in this case, that is good. They got port EFI starting in '86 on models below 8500 GVWR, and I think '88 on all models (they sold these in 3/4 ton and 1-ton trucks, too, even dual rear wheeled versions).
I had an '85 F150 with one of these, too... it had a giant 1-barrel carburetor, and was bolted to a 3+OD 4sp manual. It had over 400k miles on it when I sold it. Rear main leaked oil like crazy, but it still ran well and was still strong.