As per the links Rich attached I think you're going to have to wait another year. My Harley was built in 1984 so am going to register it as Historic on 1st April. Fairly easy process using the DVLA forms.

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10