Gauge question M35 reo

Hello all,
I have a 1952 REO M35 that i have been driving for a year with chintzy aftermarket gauges hanging below the dash for fuel and oil pressure to be safe. Im getting tired of looking at them I have Stewart Warner douglas connector gauges installed on the original dash the temp is 0-240 oil is 0-60. I have the new style sending units (MS24537-1 0-240 rubber connector temp sender) and (MS24538-1 0-60 rubber connector oil sender) when I search online it says these work with gauges that have "ms" part numbers. Is there any backward compatibility that anyone is aware of? Also on a side note my ammeter is always on so I installed a battery cutoff but I am not sure why it does this. I am not expert in electrical any help out there is greatly appreciated. - Ryan

Your auxilliary switch ("ignition") may not disconnect properly. I can play with mine and get the air buzzer to stop but the battery/charging gauge is still on, if I deliberately keep the switch in an almost-off position. Yes to the battery cutoff - that is a good safety device in any case!
As for the oil pressure, as long as you have a sender that has a range matched to the display gauge (0-60; it is engraved on the sender) you should be good. Of course, ground issues on the gauge cluster (via the screws) are always a fun possibility.

Yes, ms means military standard, and the newer gauges work with older senders and opposite. Main thing is match up the pressure ranges.

By ammeter, I assume you mean battery/generator indicator? It needs an ignition switched power feed.