The requirements for navigation lights has, as might be expected, changed as the shipping industry evolves. Your question relates to two navigation functions for the Endurance, one as a sailing ship and the other as a power driven vessel. Regulations concerning lights and shapes depend on a number of factors including size of the vessel, type of ship etc, as well as flag and international requirements.
The key date for the nav light requirements for the Endurance is 1914 when she came to the UK. At that time the requirements for lights for both steam and sail were already in force by the combined (and enacted) Steam Navigation Act 1846. Prior to that time sailing ships had rules for lights but they were not formally regulated. The Act of 1846 required steam ships to carry sidelights and a mast light. A stern light was made compulsory in 1948. For sailing ships however, coloured sidelights were mandated in 1858. As the years have gone by changes have been made to the regulations culminating in the modern Collision Regulations, which are mandated internationally with, depending on the flag, some modifications.
The key to navigation light placement is, importantly, for collision avoidance and also for other vessels to identify the type of ship and operational conduct. So, in 1914 the Endurance under power would have required a mast light and side lights, as you already identified. The mast light, in this case, should be placed on the centreline of the ship for’d of and higher than the sidelights. Nowadays there are regulations for the vertical and horizontal placement of lights. Without referencing the actual distances placing the mast light well for’d, near the mast top makes sense (but see height suggestions below). Modern day requirements are for’d of amidships. Your positioning for the sidelights on the lower shrouds around the midships location is realistic. That gives the required light pattern for identification as a steamship viewed from another vessel. She would not necessarily have a stern light because this was not required until 1948.
Turning to the ship requirements as a sailing vessel not under power. She would only need to show sidelights so for all intents would simply turn off/extinguish the mast light. Modern regs. require a stern light for sailing ships but I doubt that was regulated in 1914 for previous reasons.
The photos shown in your thread indicate portable oil lamps. The ones shown on deck could very well be spares but I would have expected the spares to be stowed away when not in use. The sidelights would have been fixed (but no doubt removable) on boards each side and I expect the mast light would have been hoisted using a halyard for ease of access (filling with oil, trimming the wick etc) but fixed in place also makes sense.
For positioning of the mast light if you followed modern regulations then it’s highly likely it reflects older requirements. Since she was over 20m in length with a breadth over 6m, you may want to consider placing the mast light above 6m but not higher than 12m, measured above the hull (uppermost continuous deck). Scaled to your model of course.
I hope this helps a little, it’s been a while since I dealt with this stuff
