Help finding headers 70 f100 with a 400m

I am having trouble finding headers for a 1970 f100 with a 400M. The PO installed the motor into it. Since i know ford used the 351C and not the 400M at that time. Do they even make headers for this swap?

I don't believe that ford ever used a 351C in truck. The 400 was introduced in a passenger car in 1971, but didn't make it into a truck for several years. In 1970, it should have been a 351W or 390 FE motor.

I use Sanderson FC-3 shorty headers in my '53 with a 400 (stroked to 434). These may work in your '70, but you should call Sanderson in South San Francisco.