So... I found an old small metal ruler and took it out to measuure my cylinder bore this morning.

It is VERY close to 3.5", so it does seem that the B18 was bored out. That in itself is pretty cool (as the car came to me very cheap), but it also seems that the head is a B20E, because it has the "floating island" center head bolt hole which falls under the valve-cover. Why are the E's popular for vintage racing in particular?

Thanks all for your pointers on this.

I do have a Harbor Freight in my area and I did happen to notice they had those cheapy wheel-rule-calipers. I think I'll pick one up next time I'm in there. It looked super-cheap, but I'm sure it's just about as accurate as my metal ruler and eyball!

Oh, a couple of follow up question on all of these developments is:

* What new head gasket thickness should I use now?

* While I have the head off, is there anything that would be good to attend to that is impossible or a hassle with it on? I noticed that one of the valves on the front-most cylinder head is a pronounced white color, and its spark-plug is much more clean than the others (very black). The ceramic white portion of the plug is even white or "clean" while the others are uniform black. It almost seems that this cylinder wasn't getting ignition!? The very back cylinder also has one valve that is medium between total black and white.