A ball bearing could replace the slider , but in my opinion it would not decrease the friction enough to make it worth while. Consider that the horizontal velocity of the slider is highest when the piston is around top and bottom dead centers. Here the pressures on slider is at it's lowest point as there is no pressure being applied to the piston. At mid stroke, where the pressures on the slider are greatest , the slider horizontal velocity is lowest.
Contrast this with the more conventional crosshead with a trunk crosshead guide. Here the crosshead velocity is highest at mid stroke and the side load between them is also at it's highest point. So the difference between the Scotch yoke and the more conventional configuration is not that great.
For reversing, a slip eccentric can be easily fitted. They are not very elegant looking, but they work well. Nno single cylinder engine will self start reliably, so the flywheel must be given a partial turn to get them started. With a fixed non-reversing eccentric this needs to be a 1/4 to half a turn. With a slip eccentric this is the same if the engine is being started in the same direction as it was stopped. If desired to reverse the direction, it just a matter of turning the flywheel in the desired direction of rotation for 3/4 or a full turn as pressure is being applied. No big deal as I normally give the flywheel a flip with my finger that is adequate to turn the engine over that much anyway.
If a more elegant look is desired, a flat spur gear differential reversing gear can be fitted. They are not seen too often so they always seem to attract attention. Chedar models made a commercial twin cylinder marine engine that used this type of reversing gear. Still have to give the engine to start in most cases.
Bot of these reversing gears can be fitted int the SC1 without increasing the height, and both will work with the scotch yoke driven eccentric. Neither of these reversing gears will allow variable cutoff, in practice few of us ever run our model engine s notched up.
Gail in NM