I keep a box of 3/8 bolts labelled "FE intake bolts"
Any time I do a swap, I throw the extras in there.
The easiest way for me nowadays.
- I stick a screwdriver in all the holes of the head and measure depth with my thumb and find the shortest, it is rarely less than 1/2 inch (more like never), but I always check
- Then I set the intake on the bench and drop intake bolts (with washers) into each hole and make sure they all have 1/2 inch or so of thread hanging below the gasket surface (with no gasket, this is just a quick measurement)
You need to check though, because bottoming out can break things quickly, but too short can also pull threads out at the worst time, when it's all together and you are torquing things down....
I often need to cut the bolts too, cutoff wheel, then dress the edge on a bench grinder for me, followed by a quick hit on the wire wheel sde if it's a big cut. If it's a little cut I just grind the end of the bolt. However, if using standard length bolts, often the combination of a lock and flat puts you where you want to be with a standard length bolt.