I have made some of the suggested revisions. Dropped off the top tier, shortened the carriage length, tipped back the front angle of the cheeks. I can NOT make further changes to other than the axles and trunnion caps - the main body is all glued now. Again, I am NOT going for historical accuracy, just a nice looking carriage that is very strong.
The threaded rods you see now are plated temporary fillers, not cut to length. The permanant ones will be stainless. (I will replace them one at a time.) All hardware not already black oxide will be painted flat black (such as the permanant stainless rod ends).
The vertical 5/16 threaded rods perform double-duty. Along with glue, they hold it together vertically, and also will secure the trunnion caps. That is why the top nuts are resessed. Bottoms are resessed to prevent sight from the sides.
In the photos the carriage is shimmed up with the wheels set next to it for scale:
In my shop, there is a slightly low spot on the floor where my equipment mounted on casters does not make good contact at one wheel and can slightly rock. That has given me the push to do the floating rear axle, as has been done on here previously on larger guns, to help prevent teetering on uneven surfaces. 5/8” square tube will reinforce the 1/2” round axle where I have to drill the pivot point, and I will split a rectangular tube to use as the axle hanger. The entire assembly will be shrouded in oak. Metal for that is on order from Speedymetals.com, as is the stainless 5/16 threaded rod and metals to fab the trunnion caps. Once that gets in I can keep going.