Hi Ratchet,
We did talk before on this vehicle. A Perkins P6 was sometimes seen in Morris Commercial trucks as a replacement for the old petrol engine, but it may have been neccesary to move the radiator forward as this engine is a six cylinder as opposed to the original being a four. You may not have much spare room in this vehicle to accomodate a longer engine. Also, the road speed will be drastically reduced as the P6 is unlikely to rev much more than 2,000, where the Morris would be near 3,500 I would think.
You were asking about a source of parts for the Morris engine, I have now remembered someone who has new parts, I am sure mainly for the four cyl. engine. It is John Walker, 52 Elmswood Gardens, Sherwood, Nottingham, NG5 4AW, tel. no. 0115 9607860 Evenings
Best of luck,
Richard