I installed these mechanical oil and temp gauges in our 68 GTX:

https://www.autometer.com/gauges/prestige-black-diamond.html

I also like the Stewart Warner gauges but the lead time was quite long and I wanted the aftermarket gauges in the car for Carlisle.

I like the dash on the 68 & 69 Plymouths, but the lack of an oil pressure gauge makes me nervous

I run aftermarket gauges in all 3 of our Mopars.

A quick story: A month or so ago I was driving the GTX. I thought I heard an odd noise, but thought I must have imagined it. I'm driving along and the aftermarket temp gauge starts to climb rapidly (the car never runs above 200 degrees), the factory temp gauge was running at normal temperature like it always does. When I pulled into the nearest parking lot, the aftermarket gauge hit 215 when I shut it down. Opened the hood, alternator/water pump belt had broke. Thankfully it didn't even boil over before I was able to get it shut off.

Thank The Good Lord for that aftermarket temp gauge! When it hit 215, the factory gauge was still at normal temperature.