Hey Victor 3, I agree with you that these are already nice miniatures (or could be) as built from the kit, the brass barrels are nicely machined and the American walnut is fine wood. What gave me the idea to change the mortar was a past post that was a discussion of the cheeks on an original Gribeauval mortar bed. The cheeks would have actually been made of bronze or iron, with wood forming the body in between them. The barrel would also have had a handle and a vent cup so I'm going to try and fashion those out of brass and solder them on it.
You can't really see it in the photos but as far as the 24 PDR goes, the person that originally assembled it just didn't do a very good job, it may be that it was a kid that put it together. The bumper on the front is cracked and screwed to the carriage in the wrong position, there are gaps between the front and rear transoms and the cheeks, there are saw and file marks on the wood that were never sanded smooth, a brass J bolt that holds a cap-square down is cracked in half, a screw that holds an axle-tree on is broken off, etc., etc,. I'm not even sure if I can use this walnut to remake the carriage out of, I'll find out when it's taken apart.
I see by your photos that you also got the Rhodes Ltd. catalog and instruction sheets; mine must be pretty old because the person that originally had them wrote down prices in the catalog. The mortar is listed at $25.00, the cannon at $75.00 and the loading tools for $7.00 (I also got a rammer, ladle and worm, all made of brass, when I bought these models).
http://www.gboreloaded.com/forums/index.php/topic,94647.