I find rebuilding MKS Sylvans to be one of their best 'features'. Since they always come with too little grease it's a
pleasant ceremony to add grease and adjust new Sylvans, and it's pretty easy in my experience.
As for keeping the ball bearings herded, I hold the pedal with the 'bearings of interest' side up, and as I unscrew the cone I keep pressure on the bottom ones. I can't remember if there's room for a wayward ball to slip between the cone and spindle, but it's never been a problem. I loosen the cone just enough to push globs of grease into the crank side, then tighten the cone enough to flip pedal the other way up & put a glob of grease into the outer bearings.
Tightening is pretty easy too, once you get a feel for how loose the cone ought to be before tightening the locknut. I usually spin the spindle to 'tighten' the cone, then back off just the right amount, then tighten the locknut.
Upon reassembly I get a nice smooth spin. The little bit of grease oozing out from the crank end seal tells me that those pedals have been properly greased and are ready to go.
MKS Sylvans are my favourite and are on most of my bikes. I just wish they'd stop 'fancifying' them by more polish and make the $#@! spindles out of much stronger steel (cro-mo?), because they bend way too easy!
As a bonus, here's some 'beausage' photos of my well-worn Sylvans after 4 tours showing how satisfyingly they wear (note flattened centre areas):

