If you are not going to pump over 8 to 10 pumps, the transfer hole size at .158 will be OK. The best mods you can do are angling the transfer port with a Dremel tool. Replacing the two round o- rings on the outside or the valve with square cross section type o- rings. This along with the adjustable cup you ordered will put you past your goal.I think you will enjoy it.
The square rings are used in place of the two standard o-rings located on the outside of the air valve. Since the square cross section better occupies the o- ring groove, the headspace air volume is further reduced. I ordered them from " The O-ring store " online. Part numbers: SN70113 and SN70016.