Valve 2100 vs 13xx

[K.O.]

One last heads up...

"My ideal is to lengthen the stroke length with an adjustable piston"

Nope  stroke length is determined by  GEOMETRY look for the Triangle and what happens to it...

and that is joined to pump effort...

also think about leverage and pump effort and valve size/pressure

the 2100 has the leverage to make the long stroke low volume higher pressure valve comfortable to use...

the 13xx unless you are willing to have your pump longer than the barrel does not have that leverage so the higher volume lower pressure approach is used.

there are threads just on this subject of course but heck you can go there at your leisure...