I think I found a guage that would work, for a pretty reasonable price. Looks like it will screw right into the port on the oil filter, and its only $19. 95. My only concern would be its holding up to the vibration.
From Summit Racing:
VDO-153009D
A space-saving way to monitor oil and fuel pressure.
Gauge, Mini, Pressure, 0-100 psi. , 1 1/2 in. , Analog, Mechanical, Each
These VDO mechanical pressure gauges are a great way to monitor your fuel and oil pressure systems and save space, too. They feature a 1 1/2 in. diameter steel case, precision-machined brass movements, and built-in restrictors to give you the accuracy and durability you want. The chrome gauges feature black numbers on a white dial, a black pointer, and a chrome bezel and housing. The black gauges feature white numbers on a black dial, a red pointer, and a black bezel and housing.
Vendor VDO
Product Line VDO Mini Pressure Gauges
Gauge Type Pressure
Gauge Range 0-100 psi
Diameter (in) 1 1/2
Diameter (mm) (Not Specified)
Sweep Full sweep
Sending Unit Mechanical
Gauge Face Color Black
Gauge Number Color White
Pointer Color Red
Bezel Color Black
Liquid Filled No
OEM Replacement No
Sending Unit Included No
Quantity Sold individually.
Notes Will directly screw into any 1/8 NPT female port.
Gauge Series Analog