I'm not positive on this but i seem to remember 1 fast Z telling something about not putting in bigger valves, correct me if i'm wrong, 1 fast Z.
If you want to use the car for street and live in Norway, i would recommend you not to go with a cam that is to big, you will need low end touqe and as far as i remember the 40 Dellorto's will run out of air at 6500 RPM on a 2.8.
I also have a set of 40 Dellorto's and i think they look and sounds great, but when it comes to that build i think the SU's will be just fine, they should handle a little above 200 HP, witch i think will be close to what you can expect with that build.
I'm not a guru or wise ass on this subject, all i know comes from using the search function and reading this and other forum's and of course my "How to" Datsun bible.
There is one selling some E31 heads on zcar.com, so if you want to have it build in US, it will be cheaper buying one of those, than shipping yours from Norway.
Chris