Confused of WHY one would ever hack up a perfectly good Reynolds flat rack ? Possible your flat rack is a different design than mine.
My bad, you fabricated a DIY flat rack. Good job, as I was under the impression it was a Reynolds with the curvature. Sorry about the misunderstanding.
The 4 OEM mount holes are for a bracket that fits to a BMW topcase. Did you already have the holes or DIY drill ?
I whipped up a custom "shelf type" luggage rack for the GS.
IMHO, BIGGER is always better for flat racks. EASY to covert back to the standard top case/tour box arrangement using shorter bolts, as the top case mounts with side flanges instead of underneath latch points.
This is not a cut-up Reynolds rack. I have one of those too (still in one piece). It will mount the Reynolds _back-rest_, which was a design requirement for this rack.
I used the holes from the factory rack as mounting points. I can mount this rack to either of my K-bikes or any other K-bike I purchase in the future (assuming it has the factory rack).
As I indicated I will mount a piece of aluminum plate to it. In theory, I could mount any size aluminum plate I want. 12x16 should be about right.
I had several reasons for doing this.
1) The Reynolds rack is large, heavy, a pain in the ass to mount/dismount and you're left with the holes to cover/fill.
2) The factory rack is not flat. That has always irritated me. The rack on my Triumph Tiger was flat, I just mounted an aluminum plate to that, no problem (I also built mounts for the Reynolds back-rest that I could attach to that setup too).
3) I thought I could build a rack, using the factory mounting holes where the load would be carried slightly forward and lower than a load on the Reynolds rack. The rack would be lighter than the Reynolds rack. And, since I'm using the factory holes, I'm not left with something to cover/fill.
4) It seemed like a fun project, where I would end up with something useful. IOW, it seemed like a good idea at the time. Building stuff beats the hell outa watching TV.
My youngest son and I are planning a (~4700 mile) moto-camping trip to CO this summer and the "back-rest" on the 22 liter case leaves a bit to be desired. Not to mention that the 22 liter case just isn't big enough for two-up camping. So I was going to either have to mount the Reynolds rack or build something else.
Tom