I haven't tried to do this particular change-over, but I doubt it would make a major difference. There appears to be enough space under the truck frame to allow for dropping it the 1.5 scale inches without dragging on the rail. The only adjustments that come to mind would be coupler mounting height and adjusting the trip pin clearance. If you know what wheels you will be using, I'll try some if I have them, and give you a more certain answer.
That said...is the passenger truck the best choice? I ask simply because it seems a bit large for a caboose (unless the caboose is a drovers car or some such converted from a passenger car). Would an express truck, like the one Athearn used under its Milk Reefer, be a better choice? (same general appearance, but a foot or two shorter wheelbase, and proportionally smaller in other dimensions- and comes with 33" wheels)
http://www.spookshow.net/trucks/cwexpress.htmlNote that those are not the same as the old MDC express truck (now also Athearn), which Spookshow IDs as a PS truck. Again, generally similar. The ancient MDC ones I have have 33" wheels.
http://www.spookshow.net/trucks/psriveted4.html
