TI'm pretty sure series 1 XR's had 170KW rather than 175kW though.

Yes they got the EL GT/XR8 extractors too, but I am not sure if the seies 1's got them as well (I don't believe they did). And no the manifold isn't worth 15kw on its own, it is a combination of better exhaust, manifold, roller rockers and more aggressive EEC programing. Its just the manifold is the most obvious change.

Yes the Explorer, GT40 and Cobra manifolds all share the same lower design so the uppers can just be swapped for some decent improvement in flow.

but it won't hurt and at least you then have a dsuitable manifold for future mods.

Initially the XR6 was the pick of the breed with far better handling and accelaration than it's heavier and underpowered brother (170kW XR8) although the issue was eventually solved giving the XR8 a much needed boost half way through the EL product cycle with the AU 185kW engine upgrade brought forward - a decision made as Tickford desperately sought to more effectively combat the VT's 179kW 5.0 litre V8 and finally out muscle the XR6's handling and weight benefits.

The EL Falcon V8:

The same old clunker was continued for EL featuring a measly 165kW (measly when you consider the Falcon six cylinder produced 157kW) although was increased a massive 0.5kW to 170kW in the XR8 courtesy of a freer flowing twin exhaust (Note: the increase in exhaust note was worth every penny!) Towards the end of the EL's life span, the AU's 185kW 5.0 litre V8 was introduced in XR8 as Tickford "desperately searched for more power" against the newer and more powerful 179kW VT SS which could also be had as an HSV optioned 195kW engine pack. Curiously, with the introduction of the 3.45:1 rear axil ratio a 185kW XR8 would be able to out accelerate both Holden offerings until the coming of age of the 220kW Gen III Chevrolet power plant - but by then you were well and truly into AU territory.

Early XR8 V8's can be identified by the inclusion of Ford's die-cast aluminium engine cover (cast in Geelong) over the dizzy / forward area of the motor while the later 185kw versions can be immediately identified by the lack of this item and the new "Explorer" intake manifold, which is distinguished by a larger plenum and slightly larger looking runners. Shipped straight from America, these engines featured much greater torque characteristics (sorely needed when you've got to lug around a heavy 4WD!) and would eventually lead to the Ford's dominance over the slightly more powerful (as far as the figures went anyway) VT SS. With this change also came a diff ratio decrease all the way to 3.45:1 making for much snappier acceleration figures

From http://www.trueblueford.com EL specifications page: