is it really necessary to get 2 egt gauges? or will one work sufficiently?

 

IF you want real accuracy 2 is great..1 for each bank. If you want to go real crazy but one egt probe on each cylinder for extra accuracy. Usually 1 will work fine though. Problems with the original plenum design dictate putting the EGT closest to one of the rear cylinders ..5 or 6. These usually seem to run the leanest and blow up first.