I bought the R4D/DC-3 package 2 weeks ago and found the same problem with missing Altimeter.
Looking at panel.cfg in these
Maam-SIM c-47 Cargo
Maam-Sim DC-3 Passenger
MaaM-SIM R4D-6
different gauges are calling Maam_R4D!altimeter
I changed the calls to Maam_R4D!altimeter1
If it´s the correct way of doing it, I don´t know, but it works for me.
Knud