The bit on the left looks like a sump flange to me, or now looking again where the filter screws on maybe...
Either way a rover 800 is not a 200/300tdi.
Does the branch of the manifold cold when starting up?
I'd suggest a stuck injector, all too common when getting them cleaned, so I have found.
You can remove, stick 12V to it while blowing through it, if it doesn't click an open it is dead/stuck.
Depends on the competition type, round here there's lots of trials run by EDORC which can handle road going vehicles, it's only if you want to do winch challenge stuff the prices gets up there.
Dirt Nationals has an interesting class structure, one team is using a gutted Jimny with stock drivetrain to learn all about speed, suspect they only spent about £4K total on it including all the safety gear.
An kept quiet!
Anyone that's stood next to a vehicle with an external 044 pump will tell you how noisy they are...
LGT has one in a 2l swirl pot in the engine bay and I can hear it over the V8 running....
You can put a bottle jack on its side, and with some timber packing spread the chassis rails that way.
Failing that, you normally just need a much bigger hammer - they are tight.