you're probably quite right Mark on the 40's versus 45's thing, and i'd all but convinced myself that i wouldnt need or buy 45's for the very same reasoning as you have stated.
my thoughts were a set of 40's with 36mm venturis's (32mm venturi is the normal uk stock) and appropriate jetting, would suffice no problem.
and that is exactly what i will be putting on my 33 16v when i junk the injection,
however, for the sud 16v, because i intend to go that bit more modified with the car, not neccessarily the motor though, and especially when a set of 45's, with trumpets, came up for grabs, from a well known race alfa, and set up as follows
Chokes - 38
Mains - 180
Idles - 60
Air correctors - 200
Emulsion tube - 9164.2
i thought why the hell not, and jumped at them!
i don't think they'll be a million miles off what i want, so maybe a little more won't hurt, but ultimatley the car will be on a rolling road for final set up anyway, and if i need to come back down a bit, i will do.
on availability, theya re all getting a little thin on the ground our little downdraughts, my advice, grab what you can whilst you can!