Hope this image is clear enough, but if not, I'll try again. Just try to figure out how to remove this type of truck. I've pried to no avail so thought I would ask before going too far.
Appears to be an old Lima or Model Power power truck. Two flexible tabs protrude from the top of the truck that have a lip at the top that fits in the bolster hole which has a lip inside it which engages the tabs. On some cars removing the underframe gives access to the tabs which can be squeezed together to remove the truck. I have been able to remove some by inserting a narrow point set of tweezers between truck and underframe and gently pry them off.
This is what the truck looks like when out. This is from my pile of unused trucks and may not be an exact match, but they're all similar. I've had luck working something thin between the truck and the body and pressing toward the center. If one peg comes loose, the truck will usually come off. If not repeat on the other tab. This type of truck is really a pain and I usually replace them if possible. Good Luck. Don