Check various online retailers or auctions such as ebay, craigslist, etc. Also some auto part stores carry new or reburbished engines for older vehicles. A great way to find one is to look into antique dealers lots. They offer a lot new items for antiques, thought they are price-e!
There are many places online that sell rebuilt or crate engines but if you want a original style engine, I would recommend a salvage yard. Many yard have website where you can look up inventory. You might also want to look at websites for fans of that style truck because chances are they know where to get parts.
Ford chose 1967 to introduce its fifth generation F-Series pickup truck. Body lines became more squared and flat side panels were accented with a narrow indention.
1968 brought a redesigned Ranchero, again built off Ford's mid size car platform, to the Ford truck line. Also, Ford's medium-duty trucks were offered with a diesel engine for the first time, but there were few other changes to any of the other truck lines. One of Ford Motor Company's top.