Bolts for Eddie heads?

Put the bolts into the heads with out them installed on the engine. See how much of the bolts/threads stick out the bottom. There should be at least 3/4 inch of threads sticking out.

Minimum thread engagement is 1 1/2 times the diameter of the bolt. Ie. a 1/2" diameter bolt times 1 1/2 equals 3/4", so you would want a minimum of 3/4" threads. (1" would be excellent if you have enough threads in your block)

I would then screw one into the engine and see how deep the threads in the block go. Then make sure that the bolts will not bottom out. Make sure that there are more threads in the block than you have sticking out of the bottom of the head when you "test fit" the bolts for length. But you must have a minimum of 3/4" to hold the torque required for a head. One inch would be great if your holes in the block are threaded deep enough. (Caution - check the thread depth with another bolt, not a wire. They always drill the hole deeper than it is threaded for "chip allowance". Chip allowance is to allow some chips to fall into the hole while tapping out the hole, so the chips won't fill the hole and the tap "bottom out" before the tap is finished threading the hole when they machine the part.)