I thought about this. The kit pushes the strut out plus the extra big hub on the 200b strut but I assumed the kit would be made with this in mind.
Can I just change the 200b hub to something smaller? R31 hub fit?
I can't speak on behalf of the company that produced your kit, but I would say it's possibly a fair assumption the kit was designed around R31 struts for a number of reasons (shortest factory strut, wheel clearance because spindle angle & hub face etc?)
The positives of the kit are widened track, but the compromise is wheel offset on the front. Some guys have used 280zx struts as they provide the best options for that kit.
The 200b kit was a good one for it's time. A $50 200b crossmember with modified mounting points, newer sway bar design, the crush tubes for the less flex. Standard unmodified control arm.
These days guys are making full replacement crossmembers, not sure why they don't also make a good fixed length control arm as well though as it's not that much additional effort. Also don't understand why the guys making the crossmembers didn't incorporate a crush tube design OR there is an easier small modification that uses a nutsert style insert that pulls into the chassis rail that you bolt to and provides a more rigid design again (searched but the exact name escapes me, will update if I find).
I haven't seen any proven data on the bits above, and everyone has their own personal preference as there are always compromises with different designs, but I prefer the stock crossmember modified to incorporate the extras I mentioned above as they cannot hurt, then run a 15mm extended control arm with whatever struts you want and still be able to fit a decent offset wheel.