Hi Chris - I didn't get carronades as it was only after seeing that post about the fittings that I realised that's what should be fitted. I had the same problem with my cannon and actually rebuilt the carriages slightly lower. Sorry I can't be of more help.
There's a very short bit on carronades here https://www.arc.id.au/Cannon.html with a general description which may help you get the correct size barrels for the kit.