It isn't hard to swap trucks, but if you buy new trucks, plan on swapping both so they match nice. And watch that your new coupler shank lengths are correct. Too long a shank and it will look funny with too much space between cars.
The heights vary a bit as well. They will couple fine; but it may sit a bit higher or lower. (Shim with a wide washer or two if too low to function; but fyi, the scale folk are always lowering cars as most "sit too high".)
Trucks are attached by a post on the truck and horseshoe clip (a kind of C clip you squeeze closed) OR connected by a rivet, which you drill or grind out. (washers, nut & bolt work too 
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