P38 Diesel Fuel Injection pump calibration or timing?

Hi everyone
Hoping someone could give me advise on an issue I'm having with the FIP.
I recently had to replace the top gasket on the VE fuel injection pump, fairly straight forward fix, accept it would seem that I didn't have it 100% aligned when I reassembled. I did the work with the pump in situ, it didn't need to be removed from car.
The result has been an elevation with my exhaust emissions, and an MOT failure.
Can this be rectified using a FIP timing kit, or do I have to remove the pump and send it for calibration?
Thanks
matteo
1997 P38 2.5DSE

If you slightly loosen the screws the top part can be gently tapped to move about, but it would be running really badly if you weren't really close.
How far off were the emissions? Have you done oil & filters yet?

The emissions were way way out, like other end of the scale...I haven't got my paperwork with me to hand but i'll confirm the readings tomorrow.
The car's actually running really well, idling fine. Noticed a bit of a stutter at top end of revs when they were testing it. My mpg has risen from a lowly 23 to more respectable 28.
I haven't done oil and filters in a while admittedly. Was sure the problem is stemming from my work on the FIP, The emissions was such a difference from my last test and the car was used little during that period.
I was aware that the top part of the fip can be gently tapped, but the vids ive seen are people with their cars rigged up to software through the obd II, and they watch the readings as they work - this isn't an option for the p38, or at least my `97, and I don't have an opacity meter machine available locally.

Top end stutter could have been the rev limiter (or fuel filter).
Air filter can make a big difference on a diesel. Clean oil will also slightly lower emissions.
EGR clean could be in order too?

@matteo Sounds like you have got the top in the wrong place, did you make sure the pin went inside the little collar in the pump, when this job is done you mark a scribe line on all sides to line it up perfectly but fractions off milometers out well not help
You are best to post this up in the range rover section Wammers is your man for this and listen to him and do as he says, he is the god on these.
https://www.landyzone.co.uk/forum/range-rover.10/