Hi Blake,
Nice find on the 13" GE!
I'm running an 11" GE forklift motor in a light car for both street and drag strip. My motor has been modified to handle more power than nameplate specs, and is working very well at 200 motor volts and 2000A.
The 13" can certainly make more power than the 11", and could power that Nova very nicely. Look at the Rocket Bike which also used a 13" GE motor, but, it was heavily modified and driven to high voltage and current using a Zilla 4k controller.
Your *stock* 13" GE can probably take up to 170V and maybe 2000A for a few seconds, but that may be pushing it.
The Z1k with a 144V pack would be max of 192 battery hp, and with voltage sag under full load, that would likely drop to 155 hp or so. You might not be satisfied with the drag strip performance.
If you are looking for much better performance at the track, you will want more voltage and amps. Get as much as you can afford. i.e. if you double pack voltage to say 288 and go to a Z2k, it would make 500+ battery hp and your Nova will be very quick.
Looking at the pictures of your motor, the brushes may be worn down enough to consider replacement. A proper brush and comm break-in would then be needed as well as blowing out all of the old (and break-in!) dust in the motor. As you suggest, increasing motor timing will help with higher RPMs.
Regarding highway speeds and motor rpm, it largely depends on gear ratio you choose for the rear end. My car is direct drive with a 2.73 rear end, at 55 mph it's running below 2000 rpm. The 11" GE has enough torque so even at this "overdrive" ratio, the car has traction problems below about 25 mph.
Your 13" can produce considerably more torque.
Wayne