Chinese stuff suffers from "quality fade' so it may have been specced properly but later deliveries often are not of the same spec. Funnily in China they price low then cut the spec to make money but feel it is better to be asking forgiveness, if you notice, rather than seek permission.
As shipments are commonly paid for ex factory you have little recourse. there is a legal system in place but you may find the factory and the local court both report to the local communist party chief who could not give a rats ar$e about the silly foreigner. This is not to say you are being discriminated against, they do the same to each other.
This is a sweeping generalisation but I remember a conversation I once had with a Mr Bao in Beijing who was a JV partner on a bid. We were faced with an impossible schedule and he said "JUST LIE. LATER WE TELL THEM IT WILL TAKE LONGER"
I had my temp and fuel gauges replaced and they are fine. Unfortunately the fuel sender I now discover is from a Toyota and the readings are weak, a full tank showing 1/4 tank, probably a mismatch in output. I have discovered that empty means empty
but that is all.
The idea about adding a resistor or even a rheostat to allow fine tuning is a good one. Unless you get good quality OEM parts you may find yourself still struggling with gauges. Fortunately the CJ-7 is a simple beast but it lends itself to inferior pattern parts being fitted.
Needless to say I will get an OEM sender from a reputable supplier in the USA and fit that rather than mess around with modifying a lash up.