F-150 -89 max tire size

I resently imported 1989 Ford F-150 XL with 33" tires . To get it licensed
(M.O.T. test) here in Finland is is required to have tyres that are listed
as alternative tire size or 2" bigger . Does anyone know what is max size
and where to get such informaton (official looking document).

Unfortunately I don't have owners manual or similar document.

Thanks

Riku.