What have you found to be a good way to estimate how much to mill an intake manifold? In some cases I've been able to use different thicknesses of gaskets to figure out how much should be cut, but this is a little different.

The intake is uncut and will barely fit (i.e. allow the bolts to be installed) the block / head combination even w/o any gaskets 'tween the heads and intake. Looking down both the bolt holes and the manifold runners shows the intake is obviously shifted up too high.

Given the cost to mill the intake, it will quickly become "cost ineffective" to guess-timate cutting off XXX, fitting it up again and sending it back again to the shop for another round of machining. So, any suggestions on coming up w/ a fairly accurate measurement for an initial (and hopefully only) cut is appreciated. - Brad