Just a thought -- you mentioned the fuel filter, but do you know whether there's another filter, inside the fuel tank? At least, there was in my '73 164, and in my current '75 164; your might have one, too.
It's a cylindrical paper element, and if there IS a lot of sediment, it could be clogging up. The element is accessible through a little plug* on the bottom of the tank -- it inserts into the end of the fuel pickup line.

If it is the same as on my 164, the Volvo p/n is 688593. It's cheap!

[ * I don't remember the details of my old '73, but on my '75, the plug is unscrewed using a ~12mm square drive. To fabricate this, I bought an expendable, cheap, standard-sized 1/2" drive socket extension and ground it down on three sides (leaving the side with the "ball" untouched) until it was a perfect fit.]