The loom is plug an play it go's strait onto the 42 pin main body connector ( the one near the N/S strut tower ) and yer the boxs again should fit just fine between models ,as for max power I think with head work you can have 220 like power from the 2.5 and yes st cam's can be fitted in the std engine but yet again a re-map will make all the nuts and bolts mods work to the max ,you could use a daz tech piggy back computer if you cant get the ST ecu I do have one if intrested but again its a large cos for mapping when the ST ecu can be had more readly.