You will need pipes from 300, are you using 4 bolt box?
I think the pipes that fit the 300 may not fit a 6 bolt box.
The pumps are not mounted on the same way on both engines and are different pumps so you will need pipes for your 300 or get some made, you say the pipes fit the box but presumably they are the pipes that came out of box so will fit the problem you may have is that if you have a 6 bolt box they were never in a 300 so no standard pipe available but if you have 4 bolter you can order 300 90 pipes and your sorted.
I seem to have the same issue. The box I fitted is defo 4 bolt, and pipes I have fit to that no probs. Pump is different fitting tho. Engine is 200tdi Disco fitted when I got it, and assume pump is from that also. Will 300tdi pipes fit?
Which pipes are you strugling with?
6 bolt and 4 bolt pas boxes are same pipe fitting 3 bolt different ,pumps have different high pressure pipe fitting ,input has hose clip so can be easily altered ,if you have 300 engine then thats the high pressure pipe you need likewise with 200