OK Tom, I cant resist
Really Big Al and Elliot are the experts here but for my 2p worth. .
With the eaton you will have really to go blow through or fuel injection both make the installation a little more tricky as if you want a blow through carb then that is where the blower wants to be
with EFI you can make up a mounting flange to a manifold (I would go 2 plane with a 1 to 2 inch spacer and remove half the devider in the middle that is if you want the supercharger sat on top of the engine .
On the other hand a blow through system does give you the freedom to mount the supercharger in different places and add an intercooler.
I presume as this is to go in a disco you want throttle responce and low end torque as you say and it wont be revved over about 5.5K. Try and come up with a set up that lets you put in an intercooler, this will be the best thing for the whole set up as it gives the engine more power and a much easier life. aim for about 6 to 8 psi boost to start with, this set up with an intercooler and mapped efi should see you to about 10 maybe 12 pai boost before you run into detonation.
on that basis, unless another block comes up for peanuts (a 3.9 is worth considering and there are still lots about) stick with the one you have and get it hot tanked and rebored and the mains line bored so it is all nice and square and get the decks squared to the crank and skimmed flat.
ARP stud kit for the bottom end, and consider ARP head studs if you have an extra £80 on the budget, either way new non stretch head bolts at a minimum leave out the outer 10 bolts on the heads.
New standard pistons should be good enough, get a set that will give about 8.75 to 9.25 to1 CR with SDI or range rover heads and composit gaskets (P6 are rubbish heads) get them skimmed flat but only the minimum skim to do the job. You want the waisted stem valves either standard size inlet and exhaust or standard inlet and over size exhaust, bullet guides and a simple pocket port job ( details on many other threads on here) matched to the inlet manifold but don't open up the ports at the inlet mating face as this will ruin the throttle responce. open up the exhaust ports behind the valves as far as you can and blend them out to the headers, but again don't go too far at the manifold face.
cam wise go for a standard road cam, or a mild perfomance one, go for one with a wide LSA (lobe seperation angle) and as much lift as you can, avoid the stage 1 v8, 101fc and MGB v8 cams as they are intended to restrict the power and strangle the engine. Install it about 4 degrees retarded.
Get the crank ground, check the rods are straight and get them shot peaned once you have cleaned them up for casting flash etc. use good quality bearings and ARP rod bolts.
You should see 280to 320 bhp depending on cam, intercooler and displacment, maybe a little more on a 3.9, personally I would avoid the 4.0 block as they are a poor quality version of the 4.6 and they are prone to drop liners and have too meny faults.
Ask away, this sounds a fun project
Mike
