I have a 400 from which the oil pan (rear sump)decodes to have come from a 73 Econoline with a 400. Does anybody know the capacity(with filter)?

 

I can't answer that, but I can tell you that it might be a large capacity. The 351M I had in a 1980 Econoline had a capacity of something like 8 or 9 quarts. I always had to double check the grease monkeys who inevitably underfilled it.