She's a beauty. Technically, loosen side screw that tightens the elevation slide. Then use top screw to adjust height, it's like a fine adjustment screw. After, getting perfect tighten side screw. Dunzo.
all sheridan streaks from '49 - 78 were technically flat tops - however the ones from '49 - '68 had grooves cut into them (they never had checkering). From early '68 to early '78 the flat top receivers were smooth - so no grooves. Then in '78, they switched to the round top receivers which they kept until end of production in '90. (after that the C9 receivers were still round but there were other changes like length and profile).