My two 6542s are each built differently from each other. Both have my bezel and insert, and both have the 4th hand and the '+' Brevet crown I modified from Rafflestime.
The one I built using the 1655 from Trusty Time uses the DG3804B it came with. I took off the crown guards, which is the most difficult part of this build. I am not talented enough to get that side of the case flat, so it looks a bit 'soft' as though it was over-polished. It's close, and passable, but not perfect. The easy part is that the rest of the setup is used as is, with the exception of the alternating red/black date wheel overlay. There are two setups used on the DG movements for the date window. The standard is set at the ETA position, while the one from some suppliers has the overlay already installed in the Rolex position. The 1655 has it in the correct Rolex position. A 6542 dial (I used the dial that came with this 1655 and put my decal and lume) , alternate red/black overlay installed and it all fits together as it came.
The other 6542 uses a case we called 'Tiger' because it came from a guy named Tiger. They are no longer available having suddenly disappeared years ago. I used this case to build my 6204 as well. It is thin, can be easily made to look thinner still, the stem is case centered, and it can house DG or ETA movement. I have the ETA 2846 slow beat, modified for GMT in it. Same overlay.
The DG3804B and the ETA handstack are both correct for the 6542 and 1675. Rolex didn't change that until later models. The DG3804B and the ETA 2846 are slow-beat so more close to original.
The Chapter ring measures 26mm, the early 6542 and 6204 used a 13mm minute hand. Later 6542s used the 12mm as is current.
I don't know that I ever heard of anyone making a sapphire bezel, and having a sapphire crystal would make it an homage rather than a replica to me.
Freddy is correct, the 115 crystal was used on the 6542, but being the only model it fit, and date window 1mm to the left (towards the center post) of later models, it is my understanding that 116 crystals were installed from Rolex as well as watchmakers. Both of mine have the 116.
The first pic shows my water slide decal dial, 13mm minute hand and red date. The 2nd pic shows the 'over-polished' side of my DG 6542, and '+' Brevet crown. The third pic is the side view of my ETA 6542.