My rear mounted Duratec is tilted forward (on the induction side) a few degrees.

Because of this I expect the dip stick to be inaccurate so to counter this I jacked up the front of the car so the engine was vertical and intended to fill the engine to minimum and then lower back so it's tilted again and see where that leaves the oil on the dipstick (expecting it to be higher as its at the front of the engine).

Is the right approach anyhow or should I set it up at the normal tilted angle? I guess it depends where the oil pump pickup is in relation to the dipstick.

And if so would the same apply to the gearbox level. This was highlighted by me removing the gearbox filler plug after it was in the car and a huge amount of oil came out (I had topped it up when the engine was level on the floor).

Also the Haynes book for a Duratec says the engine should take around 4 ltrs including filter. My filter is full but I hit the max on the dipstick after 3 ltrs.

I'd do the same.

Raise the front of the car to get the engine upright, fill to min level, lower the car check level on dipstick and scribe a new min line. The repeat for the max levels. Might take a few minutes to do, but only needs doing once.

If you have a low oil sensor this obviously won't be accurate, so might be best disabled.

What angle is the engine installed at?

I'd imaging you have to tilt it quite far before oil starvation becomes an issue - there must be design limits for cars travelling up/down hill. Also, you're using the engine transverse as originally fitted (I assume) so shouldn't suffer oil stavation on cornering either.

Do Sylva give any advice on this?

The angle comes out at approx 5 degrees.

Also I think the dip stick enters at a bit of an angle now because the line is not parallel with the min and max marks. Ive had to bend the outer sleeve somewhat to get around new induction.

Not so worried about the angle for just the same reason as you've pointed out - cars don't regularly blow up because they are going up or down hills! Its more the correct capacity, hence my concern I only needed 3 liters when I was expecting to put in 4.

Duratec HE Oil Capacity: 4.3L Oil Type: 5w-30.

I have 5 ltrs in mine due to increased capacity sump