I had lots of thinking about this today. I also don't think the 690 will fit for a variety of reasons but like you said the shock isn't the same at the regular PDS and it has a linkage. I much prefer the PDS shock because it's so easy to package and install especially in a custom application.
I am planning on building a slightly smaller main tank to replace the stock tank, maybe 3 gals. I want to be able to move the seat forward so I can sit more upright. I find the sport bike tanks force you to lean forward more. My FZ1 does this. My CBR is much more comfortable seating position because I eliminated the stock tank altogether.
I plan to couple this 3 gal aluminum tank to a 3 gal subframe tank which will house the stock Kawasaki fuel pump and sender unit. I will connect them by a simple petcock. The fill will be in the top aluminum tank and flow down to the subtank.
Building the subframe tank on the CBR was a first. There were many lessons learned. I should have never made the tank fit that YZ seat. I will most likely use a aluminum seat pan that I make like the FZ1 and have it much flatter. this should increase tank volume, seat will be way more comfy. I had a lot of problems sealing that tank because of the complexity in welding into blind corners etc, and I won't repeat that mistake. I do like framing out the subframe using the aluminum tube and will most likely do the same. By making the seat wider and more comfortable it should allow easier and simpler tank construction. Folding the tank around the PDS reservoir was a fun challenge
That big dip in the subframe top rail served no purpose other than following the line of the seat. Stupid. If I had straightened it out and made my own seat pan I could have easily gotten 3 gals out of that tank probably more.
So I think it makes sense to build my own subframe but try not to repeat the same mistake. I would like to somehow use a factory tail unit from some bike. making one was very tedious cutting and welding all those tiny pieces of aluminum and looks butch. If I had the factory mounts ahead of time and the tail light I could integrate it.
I found a swingarm for a 04 KTM. I'm going to rob the shock and forks off the CBR and replace them with the SMR units and just keep the CBR as a play bike for sunny days. I have a really nice set of dirt excels which I just installed a Heidenau K60 on. I have many triples to chose from, question remains how easy it will be to adapt the stem to the Kawasaki. On the CBR I machined bearing cups to fit the KTM bearings which worked well.
I really hope I get the bike or this will be a lot of typing for naught