OK, just taking into account what you have said in your last 2 postings, I would guess that the heat you have applied to the end cap (SA1515) has resulted in the cap expanding, with the damper plug staying in the bottom of the fork leg. Having an SA number means the cap is a sub-assembly and the individual parts are not numbered separately - hence the damper plug is not shown on it's own in the spares list. If you now look at the bottom of the fork leg, there should be about .100" of plain dia before the start of the fine thread (for the cap). If you have more than that, the damper plug is probably still jammed in the bottom of the fork leg. If the damper plug is still in the bottom of the fork leg, the bore will be about 1 3/8", whereas the bore of the actual fork leg is more like 1 7/8". If the damper plug is in place, then you will need to tease it out in order to get access to the piston - there will be a thin copper/asbestos washer(31356) between it and the bottom of the fork tube. When you get both end caps off - check carefully that both damper plugs are the same length - when we were involved with club spares, the Club had 3 different lengths available (probably something to do with the different damping required on Plus and Comp models!).
Moving on to the springs - originally, there were 2 options available, both being wound from 5/16" square wire - the lighter, standard spring(32256) being taper ground on it's OD. The heavier spring (36298) was parallel on it's OD. I have also heard of some forks having round section springs, but, at a guess, I think they may have been supplied as the only alternative after the production run of original springs had ended. 10¼" long is the sort of odd figure Douglas would have specified, but I have heard of the abutments being stacked to obtain better ride heights - so the actual length may not be too critical - providing they don't become coil bound.
Hope some of this helps,
Regards,
Eddie.
P.S. The overall length of the standard damper plug is 1" exactly.