Did Ford put 460s in these??? Nope... 1979 ford ranchero 500 for sale by owner - Franklinton, NC - craigslist
According to Rock Auto's parts catalog, the largest was 351. I believe one option was 351M which uses the same bell housing pattern and engine mounts as 385 series. It would be a fairly straightforward transplant to install a 460. The C6 overdrive would warrant some questions. You'd think if it was legit, they'd mention it was a Gear Vendors OD, or some other add-on OD setup.
