Identifying 112RD50 circuit REV #

I just purchased a 112RD50 with EV speaker in showroom condition, it contains the following numbers:
82-9 (sticker on the right side of the chassis)
BP-1600-EX/D (lower right side of the chassis)
model: 112-RD-50
chassis: 1650-RD-EX
serial number: EN10544
input: 220VAC ~50Hz. 1.1A
output: 50W. RMS
Is there any way to determine the revision number of the PCB inside ? I can�t find any directly on the board and according to the circuit drawings there are four exisiting REV numbers for this model.
From the logic and the production time (82-9) I think it should be REV D from 01/26/82
REV E is from 01/83 and shows the "mid shift" switch, my model has the normal "clean/limiter" switch so it can�t be REV E.
REV C is from 09/21/81 and REV B and A even older. So is there any way to really find out what REV # my amp is without tracing components on the PCB ?
Thanks in advance for your help guys !