250 HP wouldn't be enough? Raby's Aircooled Technology can provide the parts to rebuild that tired motor into a lively one. In the end, a much less expensive option. www.aircooledtechnology.com
110 hp is plenty for me.
Check out Thesamba.com for ideas. There are other sites that have more info on the Subaru swap but if you just feel it is under powered it probably needs to be freshened up. For the price of converting something you can get a monster type 1 or turbo your type 4.