no. all the sbk showa forks 916 (94) onward are 53mm outer diameter at both upper and lower triple clamps. well, pre pani anyway.
all the 41 and 43mm showa upside down forks used 91 - 10 (ish on later ones maybe on some) in non sbk models - ss, m, st, sc/gt are 50mm upper triple and 54mm lower.
if you got some 43mm showa forks from ssie, st, m, etc you can use those outers and put the sbk inner tubes and bits into them. the 65mm caliper spacing started with 98 sbk models (and 97 st2), so any 748/916 forks 94 - 97 will work for that. i think the sbk cartridges will have more travel than the other forks.
or you can get an upper triple with 53mm holes or bore the originals to 53mm and shim the lower with a 0.5mm shim to take up the 1mm difference.
know all wanker