Lets leave the fact that you want to bolt a R32 front to a mk3 to one side for a moment.

Yes you need a Mk3.5 Cabby front end with wings but as you have mentioned the wings are shorter due the the reinforced sill on the cabby so you need to weld the section of your old wings to them in order to them to work.
Only the cabby parts fit, no mk4 parts will.