Ran through power and torque calculations again and got more reasonable results.
Lifting 200-lb of load up a 5/8-8 Acme thread takes in the neighborhood of 3 foot-pounds of torque. Call it 5 lb*ft to include resistances from my brass sleeve-bearings. Turning that at 250 RPM will take 177 watts of power. Call that 200 watts to account for gearing and electrical losses. The Baldor motor is rated for 4amps @ 60 volts, which works out to 240 watts. So it's good I sprang for this combo as it's close to the power level I needed.
I'll need to double-check my emergency drill and socket can handle this. If it can't, I'm thinking of replacing the DIY sleeve-bearings with proper sealed roller bearings (and protecting them from heat).
Not a lot of work done today except some re-jiggering of the track-rollers to add an extra washer/spacer to increase rail-side clearance. I also welded up a pair of angle-irons into a C-channel to be used with another sleeve or roller-bearing to better support the bottom end of my lead-screw and shaft.