When you use Massey finish as a finish for a bow I really don't think the strength of the epoxy is a matter as long as it is flexable. If you get good coverage it will seal the bow like other finishes. I use 2ton epoxy that comes in a double syrenge but I have only used it a few times as a bow finish. I don't like the way it applies. I do use it to seal cord wrapped bow handles as a sealer and adhesive. Also, I've never measured the ratio between the epoxy and thinner. I mix the epoxy well then add the thinner(acetone or alcohol) to the consistancy I want it to be.
The orininal Massey finish that was developed by Jay Massey use a specific brand named epoxy and a special solvent as thinner. I would guess that not very much Massey finish these days are what Jay had originally made...but I also don't think it matters.
To remove the shine from Tru-Oil or Massey finish I do a quick spray of satin poly. Lots less work than an abrasive rubdown and IMO more durable.