Hiya,
As Skov has said 40mm below chassis rail, any higher and you will have problems with the air inlet manifold fouling the bonnet...
I haven't chopped my sump yet but you can take about 30mm off and loose about 1/2 litre of oil approx.
Still in two minds about doing it but I change my mind everyday...LOL
I'm going to change the sump gasket this weekend (along with the rest of the other parts I have stripped off the engine) so if I'm going to do it I will post the photos Sunday evening.
Sorry but been reluctant to post progress of my build just recently as I started WW3 with just asking Nathan about posting piccy's of his MX5 build (just got out of hand).
Johno