The biggest headache that I have had restoring the D series is the rust in the cooling system. With a crack behind the carb, perhaps the cooling system has been drained many years and this causes rust flakes to form. Look inside the radiator. Maybe take a magnet to fish for rust flakes in the top tank.
Loosen the oil drain plug and observe what drips out. Hopefully just oil.
The 5505 head showing on the right side is the high compression head.
The foot clutch sometimes does not release good. Take a strap, twine, cord, etc and tie the clutch disengage. With the tranny in neutral, see if the belt pulley shaft will turn.
Two hyd levers are the better setup.
Take a pen lite and look in the fuel tank for rust.
Look for rear rim rust around the valve stems. The rims may be rusted in the inside.
A distributor will be easier to maintain that a mag. 12V is good.
I have found that the crack behind the carb is weldable with a MIG if certain procedures are used. If you get to that point ask me how. An AWF front axle make the DC a nicer tractor to run.
Look at the eagle hitch and see if the latch mechanisms are still there and not broke.
Check around the brakes for oil seals leaking.
An original upper 3 point link is a valuable feature.