These are quite small and narrow for what they are, and will fit where an essex used to be. You will need to run it on an aftermarket ecu, power wise you should see 330hp from the 5.0, the 5.5 nearer to 375hp. Then there are the supercharged versions if you want more power.
The auto box these come with has an off the shelve controller available that uses paddle shifts, the boxes themselves laugh at big power.
The Cologne V6 is the natural choice, successor to the Essex. Cosworth modified it and their 2.9 litre 24 valve version was rated at 215mph, giving Ford's flagship Scorpio Ultima luxobarge a good turn of speed. The Ford Sierra XR4x4 used a strong Ferguson AWD system to give improved roadholding and to lay the power down more effectively. I believe some enthusiasts swapped out the original Cologne for the Ultima's Cosworth lump. Minker further modified the Cosworth Cologne and Turbotechnics double-turbo'd it which took it to 600bhp!!
If you could get the Cosworth 2.9 litre and the XR4x4 transmission / running gear that would potentially be a good combination.
If you could manage with more modest hp's then perhaps the (Rover) V8 would fit? Some later versions of up to 5 litres capacity were used in TVRs, there are some salvage dealers who specialise in breaking TVRs.
Scim chassis can take some power with no mods due to decent rear suspension and axle. the biggest bang-for-buck setup that will be easiest to fit in terms of off-the shelf parts variants to make it fit, I.e. exhausts, sumps etc. Will be either a small block Chevy or ford Windsor. You’ll get 350-400hp without even trying, and torque for days.
My first sergestion would have been the 3.0 jag V6 from the s-type and X-type as well but you say it's to big? In the X-type it's mounted transverse so I wouldn't of thought that would have been that big and there cheap as chips Other options on V6 would be fords mondeo st Alfa Land Rover freelander/MG ZS Nissan 350 Toyota do one that lotus use or Lexus do a V6 As for power I'm sure the jag is 240bhp and with good torque the MG is only 180bhp mondeo is 220 And there all quad cam set up so I'm guessing if ones to big there all to big Again I have no idea what your putting this in so I don't know if a straight 6 is also to big Which means the only option is a highly tuned 4 pot of some sorts or maybe a 5 pot
1992 240 Volvo T8 1994 BMW E34 M5 1999 BMW E36 sport touring 1993 Volvo 940 TT8 1971 VW bay window 1999 Mazda 323F 1987 Jaguar XJ12 All current
You can build an engine to produce 500BHP but it won't necessarily make a three ton vehicle that is as aerodynamic as a house brick overly fast. If you look at Caterhams and other types of Lotus 7 replicas/locost cars, you can build engines to produce,around,150BHP at the wheels and there won't be too many other cars out there that will out perform and out handle you. The O.P hasn't actually said what the engine is likely to go in, maybe that's a fairly important detail?
In the case of the SE5/5a, the only quad cam that fits easily is the Vauxhall V6 - helped by its narrower 54 degree vee angle. Of course others will fit but you start compromising footwell space as the engine is already set a long way back (the rear 2 cylinders sit behind the effective firewall/bulkhead). That gives you either 215-220bhp or so on stock management or a bit of porting and aftermarket ECU has given 260+ - and still on the original cams.
You can squeeze an OHV V8 (Rover, SBC) in there with just a little bit of tickling.
If it was the SE6 series, you’ve got another 3” of width in the bay - that’s enough to lob the Lexus V8 in there.