Anyone know how much a set of 121 delivery valves are worth?

 

121 don't exist I don't believe. 131 is stock 165/175 horse pump and 181 are stock 180/215 pumps.

 

They do exist I pulled them out of the injection pump of a 98 12 valve I recently bought. They come factory in 8.3L cummins engines but I can't find any pricing on them. I know they flow a hell of a lot of fuel though to much for my application