Head gasket and high pressure oil leak!

Hi, so I have a 1999 defender 110 TD5.
Recently it developed a pressurised coolant system which was a failing head gasket leading to exhaust in the coolant.
So I have (following the haynes manual) replaced the gasket.
I happened to have an AMC head lying around so stuck that on instead of the original 10p head.
I had the head pressure tested and skimmed by a local engine shop.
When I came to start her up today I got it running on maybe 3 cylinders and shooting high pressure engine oil out from under the exhaust manifold. I assume this is from oil getting in a cylinder and getting ejected out from the head gasket.
Has anyone experienced this before? Is it indicative of a specific mistake I may have made.
The only thing I can think of is that I didn't quite get the stage 3/4/5 (90/180/45 degrees) tightening right or possibly I have also just captured something under the gasket at the last minute.
How would oil get in the cylinder?

It is worth noting that I also did the following at the same time (because was swapping heads)

• inlet manifold gasket
• exhaust manifold gasket
• injector seals
• various orings and copper washers on dipstick, tensioner etcf

Any ideas before I start from scratch and removed the head again tomorrow arvo?

are you sure its from head gasket and not turbo pipe or centrifuge

I believe it is not the turbo banjo bolt and I have not disturbed the centrifuge and it appears to be tight. It is a proper high pressure spray. Covered the driveway in 30 seconds and was spraying up to a metre out of the engine bay. I've just read through the Rave and it matches with the haynes guide and appears to be exactly what I did.

Thanks James for the suggestions. Okay with the help of the trusty assistant (wifey) I managed to observe first hand - it is the oil feed pipe to the turbo, but down at the far (untouched end) actually from the pipe. It must have split during the various processes.