It appears Stryker kept the discrete component style of construction and your main board seems to be similar to the 440 (like all of the big Stryker radios.) That being said and according to the following information VR14 is the modulation pot, VR21 is the AM low power and VR13 is the high power adjustment. Interestingly, I don't see VR 21 on the PC board layout PDF so you could be right about VR16 being low power. Hmmm. Just take a fine point sharpie marker or similar and mark the pot and board with a hash mark
before you adjust them in case you wanted to go back to the original settings.
http://www.cbtricks.com/radios/stryker/sr_440hp/graphics/sr_440_hp_alignment.pdf
Another site references the lack of a low power adjustment and required some additional components to bring down the carrier. Obviously a few variants of this board are out there.
http://www.radiomods.co.nz/forum/viewtopic.php?t=1925
The Stryker 497HPC is one of my all time favorite solid state AM radios by the way. Got a couple in my vehicles