Help with flywheel bolt removal

[tcane]

I am trying to remove the hex head bolts on the flywheel connecting it to the crankshaft on my 1977 300D. Two of the hex head bolts are missing part of the side (the way I found them, it looks like they just dissolved away!) and the correct size Allen head wrench just spins freely in the head.

Unless someone knows a better way, I am going to remove the flywheel bolts by drilling them so the head comes off and then back out the shank with the threaded portion (I hope to use a pair of pliers, but I am ready to drill the shank to fit an easy out tool into then back out the remaining part of the bolt).

What is the approximate diameter of the shank on the flywheel bolt? The flywheel bolt is the waisted shank type that stretches when torqued and is smaller in diameter then the threaded portion of the bolt. I believe that I should use a drill bit just larger than the shank to remove the head and avoid contacting the side of the flywheel because the flywheel is balanced. I have fractional, metric, and numbered drill bits - so I have the correct size bit if someone can tell me the approximate size of the shank.

Also, how hard are the flywheel bolts? I have some good drill bits (Snap-On), but I can get harder drill bits if needed. I have seen that M-B uses some very hard metal for some parts/fasteners and I do not want to start the job only to find that I need better drill bits by finding out the hard way because I messed up using the drill bits I already own (my drill bits are sharpened properly) and, thus, make the job harder because I have to correct my mistake first and then use better drill bits.

Thanks,
Tom