i was wondering about the voltage limiter as well.
if it had just been the water temperature gauge, i have seen the typical greenish/gray, or grayish/green deposits on the sender throw the temperature to the coolish side.
when a guy polishes the sender to a bright brass finish like it was when new, the gauge returns to normal readings.
as this tarnishing occurs over time, it takes awhile for it to actually affect the gauge reading.
it seems it takes a "just enough" amount of this deposit to affect the reading, otherwise, it reads as it should, until the "just enough" tarnishing amount of deposit is reached.
as to the oil pressure gauge reading low, i have seen small pieces of engine gunk get into the sender, causing the gauge to read low.
as these are impossible to clean out, a new sender is the only way to fix this issue.
however, all new senders are not created equal, so when a guy replaces the sender, all i can say is "buyer beware".
now with BOTH gauges reading low, it almost points to the voltage limiter as the problem like stumpy says, but before a guy rushes out to buy one of those, check the limiter's connections to be sure they are clean and tight, and also check the dash grounds to be sure of the same.
just my experience and opinion over a 55+ year span in life working on this brand of toys, and experiencing the same issues.
your mileage will vary.