as the gcr's concerning fork size's for Period 5 start with the sentence " unless otherwise contained in the machine's original specifications...". if the Yoshimura bike in 1980 was originally fitted with 43mm fork tubes then there would be no problem in useing them today. this would also apply to any replica's of the Yoshimura bike.
There are those who do, those who used to do and those who never did.. why is this 3rd group always trying to convince everyone they know best?
HHH in that case you would not have to build a replica of the whole bike,just build a set of 43mm forks up and say they are 43mm replica's of the factory GS1000R 8 hours bike.........it's no different to what every one dose with the 41mm forks any way!!