Hello. Both versions look quite good when erected and in place, although the built-up version needs weathering over the three airbrush swipes the factory worker gives the inner pit. They can both be improved with details, careful scenicking around them, some decent weathering, and so on.
The built-up needs a hole roughly 1/2" larger in diameter than the kit.
The kit is not my first choice, having built one and fiddled with it, and that is by quite a margin. It looks good, don't get me wrong, but there are more complaints posted here, and questions about how to get it working properly, than you can shake a stick at.
If you have some assembly skills, some fix-it savvy, and don't mind motorizing it yourself and tweaking it to work smoothly, you will doubtlessly have a nice quiet and good looking model. Mine weathered well, and once I had it working reasonably well, it worked smoothly, reliably, and quietly! The built-up is much noiser. The difference probably comes form the fixed power supply setting for the built-up, and then it depends, I believe, on the actual voltage delivered to the motor. If less, is my theory, it would probably quieten down. That is the advantage of the kit because you can dial in just enough DC voltage to the motor to get the bridge turning and you will barely hear it.
Big difference...about US$200 after both are up and running electrically, in favour of the kit.
Any other questions?
Several things:
a. become thoroughly familiar with the various parts, their order of assembly, and with the instructions. I feel that some modellers are missing a step that makes the kit a poor performer.
b. when you deal with the lower pivot assembly, with the wipers and everything, take your time and do it right. You may have to fiddle a bit. For example I didn't trust the copper wipers to stay aligned with their brass rings over time, so I used thin plastic spacers or washers on the bottom edges of each ring to ensure that the wipers would not be able to fall sufficiently that they lost contact. As you would expect, these washers were a few mm larger in diameter than were the brass rings.
3. for whatever reason, my bridge wobbled something awful, and I was quite careful to assemble everything. In the end, I finally decided to place styrene sheeting in the form of two rectangular shims between the large metal washer at the top of the pivot, directly below the pit, and the nether side of the pit. Two, one on each side of the pivot. These had the effect of taking up some excessive slack or tolerance above the large washer that was allowing the bridge to wobble quite badly. This fix worked quite well, and the bridge rotated nicely thereafter, including weighted with a locomotive.
4. You may have to insert thin cardstock shims between the electric motor and the closest housing wall in order to force the meshing of its small gear with the large black ring gear fixed to the pivot post. Trial and error will reveal to you if this is a problem after you place the TT in its recess and try it out. If it rotates 360 deg, you are fine.
5. lastly, but by no means least, your inner pit wall may not be as circular as you would hope. I found that my bridge would not turn a full 180 deg without seeming to encounter the inner wall of the pit at some point, thus binding and causing the bridge to catch, then jerk free. I did my best to grind away what I felt were the troublesome areas without causing too much damage to the thin styrene, but in the end I gave up and only rotated the bridge in an arc roughtly 90 deg, which was sufficient to get my locomotives in each of the three bays opposite the approach.
You are referring to a braced arch that really isn't an arch, but two vertical posts with short diagonal swaybraces, and a horizontal crossmember? That structure was the contact point on the bridge for the electric motor below the operator's consol...the drive for the turntable. It has no purpose for you model other than to look prototypical.
At the centre of the crossmember is a swiveling short arm to which the cable came from a pole near the pit edge. So, the bridge and locomotive rotate below the cable that is suspended between the pit-side pole and this swiveling contact arm at the centre of the crossmember.