For backboxes, I believe Remus were the suppliers of the TTE boxes that came on the SR, so it may be worth checking if they still make them. I think there was some discussion about it ages ago. If not, then keeping an eye out for someone selling Japanese exhaust backboxes may be your best bet, i think theres one or two for sale in the Parts for Sale section. Idrees is selling a 5Zigen Fireball backbox, but it'll need some metal and a pipe welding to it. I might just be competing against you if anything worthwhile does come up though If you don't have the materials, money or time to rig up a proper cold air feed, or getting a CDA enclosed filter like in the picture above, then yes, a panel filter will be your best bet. It'll also be worth checking into local scrappies. A certain year range of Corolla had the same engine as our trusty N/A's, but a different inlet manifold, the part responsible for regulating air flow into the engine. Find one of these if you can, and buy it for no less than 50 quid. Anything more is a rip-off. When replacing the standard inlet with one of these Corolla inlet manifolds, the 4EFE gets quite a nice boost to performance all the way through the rev range and general top-end grunt. I'm sure someone will come along and tell you which year of Corolla it is (95-99ish?) I'll see if I can find a picture when I come back later today. Hope this helps!