Sutherland says: YES, both the SL P3 and the V4 take 25 loose balls (in both top and bottom races, so that's 50 balls total) and size is 5/32".
IF your races/cups are in good condition (no pitting, "brineling" or grooves) I'd reco you use Grade 25 balls as these are best quality but also "through-hardened" chrome-alloy steel.
IF there are MINOR wear areas in any of the contact surfaces some of us use "lower grade" (less hard) balls such as Grade 300 in order to squeeze out some more life from a HS, but it's a judgement call. And eventually you will need to buy a replacement HS as wear will continue and get worse

PLUS best practice is to ALWAYS replace all the bearing balls at once and don't mix old balls with a few new ones. They will not "play well" with each other Last trick with loose balls is use a "tacky" grease that will help hold them in place or you may lose them during (slow and careful) re-assembly but work over a towel or rug so if they go flying again they will fall (and stick!) where you can find 'em