A boxer manifold is good but bare in mind tein SU's with correctly setup are good for 220BHP.
Stick with SU's if your adamant to keep carbs. However EFI can be played with. The art is to get the FULL Recepie right and it will be a grand engine. just throwing in a Cam and it'll be alright isnt the way forward. P.S 4 Su'd means you need to get 4 identical Needles!!
LOL, looks like my quest for power might be due to the fact its down on compression, see my other post . My indie says these are a nightmare to setup so thats out