I am now busy with a 1987 mini 1300
can anyone tell me will it be tax free next year

Nope, it has to be 25 years old...
There are some insurance companies that will take it for an oldtimer if its 20 years old, so you will be able too insurance as oldtimer, but you will have to pay tax for 2 more years. (but its about 7 euro a month...)