Yes... I was talking about the 4-2-1 setup and John the engine builder said "I thought you were building a race engine"...
Apparently race engines use a 4-1, so he told me to make the primaries 45mm and 865mm long, blending into a 63.5mm collector.
I was quite happy with that as its going to be less of a job to sort a 4-2-1, I will loose some low-end, but I'll have 4/5ths of F**k all low end anyway.