Dave, runners are pretty easy to fit. Had the same seats as yours in our DRB and we used Van seat sliders. They are generally very slim mounting. A Search of the wreckers will find them for a good price. Make sure though that they are double locking, ie, the lever engages lock on both left & right sliders. Some sliders only lock one side and are not as strong.
That's not going to be the problem.
Being 1998 vintage, I'm guessing you don't have a dropped floor DRB. Does your floor kick up where the seat mounts, or is the floor completely flat from front where your feet are, right to the back where the seat is?
If you have standard floor(not dropped), I expect any sliders will make the seating position too high. If you have a dropped floor, then ignore my ramblings as you will have plenty of room for sliders.
With our DRB will cut and welded recesses where the sliders were. The seat height was only a couple of mm above the remaining floor so that it would slide back and forth. Only raising the seat a mm didn't impact seating height. And we could still fit catalytic converters under the seats as we didn't have the floor completely dropped.
I've always been bemused that in the old days, most Cobra's never had sliding seats and they were engineered fine.
