That happens all too often. Vernon, the previous owner of Big Blue, supposedly had the engine rebuilt. But that took 4 years! And, when he got it back it was low on oil in 20 miles. He took it to another shop and they found no gaskets on the valve covers, and lots of other problems. But after another $2000 they got it running pretty well.
When I decided to go EFI I pulled the engine and did a leak-down test and found over 50% leakage on 2 cylinders and way too much on all cylinders. Then I discovered salvage yard marks on the valve covers.
So it looks like after 4 years and he started pushing they went to a salvage and got an engine, slapped the Edelbrock intake and carb on it, painted it, and called it new.
Gary, AKA "Gary fellow":
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Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI