i know this is an old post and you may have purchased already but i bought a 'universal' large front mount from eBay a couple of years ago for my RX7, i only paid about £110 and it was huuuuge! i was really impressed when it arrived, the welds were pretty good and so was the alloy quality. Its now on an Evo 4 in Norwich.
i cant remember the place i bought it from but their feedback had comments about how good the quality was which is why i went for one.