How much can safely be safely takin off before changing fitment of the intake

I've gone as much as .060 and still fit a Factory Edelbrock six pack manifold on, had to eliminate the front and rear manifold seals and just bead them with silicone, factory side port gaskets fit

when you take the intake manifold mounting bolts off see how dead centered the threaded holes are in the manifold holes and also, how thick of intake gaskets are you useing?

Probably no more than .020 A lot of times aftermarket intakes have to be cut even with just a clean-up cut on block and heads, especially edelbrock intakes. I wish I had every $100 bill i have spent on having edelbrock manifolds cut so you can get the bolts to go in without tearing up the threads in the head.