The wheels on the carriage, not the chassis.
The small cap screw bolts will be replaced with solid rivets.
The wheel axles are yet to be made and pinned. (the Philips head bolts will replaced with solid pins and washers, and held with taper pins.)
And just to remind you of the appearance I am aiming for…
I do wonder about the original colour of these 1866 cannons. The rusty iron colour has some attraction, but I would be certain that it is not original. So far I have had no luck finding out what the original colours were.