Ah, the Riceworks kit… Very nice. I keep promising myself one of those to build. But I have a couple of Connoisseur ones to build first.
Now, being Iain Rice designed, then it is almost certainly designed for compensation. That looks like the hole for the compensation beam axle between the LH and centre bearing holes. But for compensation *or* CSB, you will need to remove that hornblock cut-out.
I’d change it to CSB myself, but that’s because I’m a “convert” to springing and have no fears about doing it. I’d split cahssis it at the same time, to help further with pick-up, like the 2FS boys do.
To talk further about springs, removable fixed axles, and so on, a little more background would help. Are you going to compensate or CSB it?
And for the drop-out wheels question, what type (manufacturer) of wheels are you thinking of using?