Hy MatBrindley, welcome, is your 261 in a big truck,or has it been transplanted into a small truck? Do you know the history of the engine/truck? Passenger car and light truck engines use a fibre cam gear, large truck engines and I believe all 261s use an aluminum cam gear. The fibre cam gears can fail, teeth can be ripped off of it, usually when this happens the engine will never run until the cam gear is replaced. It is possible that someone rebuilt your engine and used a fibre cam gear in place of the aluminum gear and that fibre cam gear has failed.
The only other thing I can think of is if you ran the engine with old gas varnish may seize some or all your valve stems in place. Take your valve cover off and check for bent pushrods. Good luck and please keep us informed of what you find.
Last edited by 3B; 06/11/2022 4:08 AM. Reason: Added an "r" to you making it your
