This weekend I soldered the frame back onto the radiator, and it appears to hold water just fine. I finished wiring up the ignition and headlights, poured some two-stroke gas down the carb and after determining I had the timing a classic 180 degrees off, got it to run!
It does look like I will need to change the manifold gasket as there are some leaks on the back end. I'll take a wrench to the manifold to see if the bolts are loose.
It seems the clutch does have some grip, from cranking the motor the flywheel needs to "wind up" a partial turn before the driveshaft starts to turn. I've never actually seen this before - the clutches on our farm tractors are more like a light switch so I'm not sure if this is a feature for the two-speed axle or something else.
Since I got the motor part on the run, I pulled one of the front hubs to look at the brakes. One of the brake shoes is rather thin but I think I can reuse it. The wheel cyilinder is pretty crusty with powdery corrosion behind the dust boots.
Any idea what the part number of the wheel cyilinder is? I saw on another thread someone mentioned the part number NAPA 15315 but I'm not sure if that was in response to my question there. I presume the wheel cyilinder size is based on the piston bore size?