When I am messing around with OFS I usually keep them at maximum 80Mb..usually bigger partitions will mess up (at least for me).
It is possible to use FFS with 1.3 and if you have an installationdisk that came with your harddiskcontroller it will fix it for you, else it is some extra work for you... but it works. Read the 1.3 dos manual and it will explain some of the things you have to do.
Bent