Any of the 100PT, 105PT, or X101 could be used with the DRG Simulclass (the X101 would have made the amp a DRGX technically).
But @NineShallDie is almost surely right that it's a 105PT. Not sure how much it actually matters; just discussing it. The 105PT has the highest plate voltage. 100PT the lowest. X101 in the middle. The X101 was an upcharge. The early C+ may have used the 100PT. Most later C+ used the 105PT, but they just grabbed whatever was available really. I have a Mark III with a 100PT that seems to be original and Mike B just seemed to shrug about it when it was in for service. So a C+ in theory could have either (but most likely the 105PT).