The naval guns were mounted as Swivel Guns on the usual 'tuning fork' design rail mount.

I do not have a design for the la Ordenanza de 1783 cañón de á 4, de montaña carriage, but I will search my copy of Morla text to see what I can find.

The chambered naval pieces appear to have been used by the Spanish horse artillery formed in the 1790s. The engravings seem to show an a la Rostaing style carriage with a steep angled trail and a continetal style limber with box. See:

http://www.napoleon-series.org/cgi-bin/forum/archives_config.pl?page=1;md=read;id=129911

Later period refs are re colonial areas - again, no idea as to carriage design.