Modern ATF (Dex 3 and newer) is 10w or 5w or even 2.5w (Dex 6). Type F is 15w or 20w depending on who blended it to which era spec. Type F will eat your fork seals. B&M Trick Shift (super expensive "performance" ATF) is actually just Type F...

Can you add any to your existing fill? Yes. An ounce per side at a time, with test riding in between each addition. If you hit 18oz per side, assuming you had 14 oz per to begin with, and it still feels soft or is bottoming out, drain them and go up a weight or two on your fork oil. You can get up to 40w from Bel-Ray. The thicker the oil, the more likely you are to blow out a seal.

I use Dex3 in my Savage. Drop out the forks, drain them, collapse the upper tubes into the lowers. With springs out fill to the top of the upper tube, extend forks, add guts, bolt back in. Ride is still a bit soft for my liking, but, I'm used to springer and girder front ends. I hate fork dive...