Hi have a 4.4tdv8 that’s had the hpfp replaced but is flagging up code p0087-21 fuel pressure to low.
Could this be related the timing of the pump if wasn’t correctly timed?

I don't know but it sounds possible. Are the harness plugs to the pressure sensor and pressure valve on the rails connected?

Let's see what others make of it. 2012 Vogue TDV8 in Aintree green over sand

As far as I am aware the high pressure pump just builds up the pressure and the ECU does the rest, firing the injectors and controlling the pressure via relief valves. There is a valve on the drivers side rail at the back and one on the pump. No timing for the pump. Maybe try bleeding for any air in the system and good connections on the plugs.
On a friends Ford common rail diesel which had had loads of money spent on recon injectors as it would not start I diagnosed the injector rail pressure relief valve was stuck open and therefore the required pressure was never achieved. New cheap Valve and instant start. 2007 TDV8 VSE
2003 TD6 gone.
2002 P38a gone
1999 P38a gone
1997 p38a gone
1993 VSE gone
1992 VSE gone
1966 Series 2a with V8 conversion gone

In the workshop manual it says to lock the crank and align the woodruff key on the gear so one imagines it would be difficult to mess it up. I'd expect it to run very poorly if it was out as it is timed on the inlet cam gear.

All just guesswork on my part. As above, maybe it is just a sensor? 2012 Vogue TDV8 in Aintree green over sand