Bit of a stupid question but I’ve never ridden a board with this shape or setup...

Recently was handed down a Santa Cruz Saved by the Shark fish-shaped complete. It has Bullet 147 trucks, which is a little odd given that the board is 10” wide. The trucks are fine for regular use (nice and curvy) but I recently threw on Waterborne Surf and Rail adapters, which are taller and much, much looser to skate on. I’ve used the adapters on a number of boards with no problem but on this setup it’s way too unstable and I’m wondering if it’s the truck width. Thinking of just grabbing some Indy 169s (I don’t need overly carvy trucks, the surf and rail adapter do the work there), but wondering if that would help in the right way.

Here’s the thing, while the board is 10” wide at the center, it tapers in on the nose and tail (never ridden boards like that)...given that, should I be basing my truck width on the widest portion of the board or the nose and tail? Trying to understand why 147mm trucks would be stock on a 10” board to begin with.