the Marines have grabbed my attention though as i seem to remember the Marines in 1870 with the peculiar 1858 working cap...like a scottish bonnet and wrapped in a leather jerkin/sheepskin............do you have any pictures of these??
Yup, I do :


However, these boys aren't Marines (or
marsouins, as they were popularly known) : they are sailors seconded from the fleet and formed into field battalions to help defend France during the 1870 Prussian invasion. The goatskin jerkins were not specific to naval troops, by the way.
The
Infanterie de Marine were regular infantry battalions meant for overseas deployment, not seamen : they didn't crew ships and fought on land in the colonies (or soon-to-be colonies), which were then placed under the authority of the
Ministère de la Marine. The 1858 cap was only issued to sailors : the
Infanterie de marine wore the shako when in full dress and the kepi for fatigue and campaign duties (it seems dubious that the shako was ever worn for active campaigning in China or Mexico, although regulations theoretically demanded it). The
paletot was effectively a double-breasted frock coat, and here's a reasonable picture of a
marsouin in full dress during the mid-1850's :

The uniform would not have changed much by the time of the Maximilian adventure : the kepi would have been worn on campaign instead of the shako, and white gaiters were used, both under and over the trousers. The shell jacket was also used in the field and a sketch by captain Vanson shows a Crimean war Marine marching to Balaklava in 1854 wearing a shell jacket and blue/grey trousers piped red with an uncovered kepi.

Here's a slightly later depiction of a Marsouin in the 1870's : the frock coat had become slightly shorter by then, and the accoutrements are post 1867, but the overall look had not changed significantly :

The yellow epaulettes were the trademark of the naval infantry and looked very similar to the ones worn by line infantry voltigeurs :
Here's what sailors/seamen looked like in the 1850's (the 1858 cap gradually came to replace the hat, although the latter endured well into the 1860's) :

Re the FFL/line uniforms, I assume you are familiar with the following plate by Leliepvre :

The full dress uniform is that of the 1860 regulations. The field dress is what most French soldiers wore while campagning in Algeria, China and some parts of Mexico. Epaulettes were commonly worn on the shell jacket, and they make for more colourful uniforms anyway so I would definitely sculpt them on ! (well, if I could sculpt that is...)