Freakin' Bolts

Yes Sir......But it will give you the diameter & thread pitch. For the length you could just measure . Would a 1953 TSM list bolts & nut sizes ?

 

I would also recommend removing the fender for easier access.

Welding a washer/nut is my preferred way to remove stubborn broken bolts/studs. It helps expand the broken section with heat, then shrinks slightly when cooled, helping loosen it. Unfortunately yours is broken off flush, which adds to the difficulty getting a good bead.

 

I can't believe that bolt broke. Usually the valve cover bends quite a bit before bolt failure. Maybe it was previously stressed?

 

The original bolt has a shoulder on it to keep you from collapsing the tappet cover by over-tightening. Likely, the bolt bottomed out to the shoulder, then broke when over-tightened.
If you can't find a shoulder bolt (like a lawn mower wheel uses), you could use a short piece of pipe as a sleeve to serve the same purpose.
-Donny

 

If you have not started, arc weld will not stick to cast Iron as mentioned above. Common method on exhaust manifold bolts that break is to weld a flat washer to the broken stub/bolt making sure o.d. is great enough to weld a nut to the washer. Nice thing you have lots of room try a thick fender washer and go up to a 5/8 or 3/4 nut weld all around. The welding process may allow the bolt to be easily backed out using an impact set a very low pressure, or even a battery powered impact with short bursts.
For penetrating oil try kroil.

 

I would try and find a left hand drill to drill it out with. I have a set of them and have had good success with the drill catching the broken bolt and spinning it out while drilling. If you want I will send you one of mine, let me know. Good Luck Don.