The front end is not from a 84 RM250, they had a drum brake.. It's an '85 front end
Unfortunately, if you wanted to race Pre85 you would have to fit a 43mm disc front end from something other than a RM made and designated as a 1984 model
(or)
find the almost unobtainable 84 RM250 front end
(or)
An 84 RM125 front end and modify it internally to deal with the weight and performance of the 500
I'd still buy it though as i've got a few spare 43mm TLS 84 front ends.
Problem is i just dont need anymore bikes, let alone a 500cc 2 stroke!