You're correct, the 25 is an 8086...well actually I don't know that 100% but the model 30 was an 8086, and the 25 and 30 were supposed to be the same but in different physical forms.
I'm sure it's an 8086 though.
The 8086 versions of the Model 25 and 30 ran at 8MHz. Other than looking inside, if your Model 30 has a darker band around the bottom of the case (instead of all beige), it is the 8086 version. Likewise for 720Kb floppy drives (which can be upgraded to 1.44Mb with the right components) or seeing the back edge of the system planar being stepped.
That version was unusual, because the PSU had a larger motherboard connector (all versions of the Model 25, and the Model 30 286, had the same size connector, with the Model 30 286, Model 53SLC2, and Model 55SX sharing the same PSU). I have speculated that the 8086-based Model 30 might have been intended to have the Model 25 planar (and to be in what became the Model 30 286 case, most case components shared with the Models 53SLC2 and 55SX). The 8086-based Model 25 planar was produced later, can use both the 20 and 30Mb HDD (the 8086 Model 30 only can use the 20Mb), handles the 1.44Mb floppy upgrade a little bit better, but didn't have an RTC on the system.
The Model 25 286 and Model 30 286 shared two slightly different planars. If you have a monochrome Model 25 it is the 8086 version (although there were color CRTs for this level too). Also a 720Kb floppy drive is indicative of being 8086-based.
There was also a Model 25SX, but no compable level made for the Model 30...