I did a full set of guages on my RTV X1140. I did oil pressure, oil temp, water temp, HST fluid temp, volts, boost, EGT's, tachometer, and I am working on a HST pressure guage setup using a GlowShift HPOP guage and a older ford ICP sending unit to monitor HST pressures in real time. You will find the port and factory light sender are both 1/8 BSPT and almost all aftermarket sending units for oil pressure are going to be 1/8 NPT. GlowShift makes tees that have a male 1/8 BSPT thread that goes into the block and has a female 1/8 BSPT thread on the opposite end so you can reinstall the factory sender. It also has 3 1/8 NPT ports on the sides for any aftermarket sedners you want to use.
GlowShift 1/8 BSPT Male to 1/8-27 NPT Female Hex Thread Adapters Make It Easy to Add a Factory Sensor and Also Install a Wide Range of Aftermarket Sensors.
www.glowshiftdirect.com