Thanks everyone.
I'll give all those suggestions a try.
Are these tapered holes in the block? Is that what tightens the plug, or
is it the plug expanding while being tapped in?

I'm a little reluctant to put a bead of RTV around the plug. If I do that, I'm sure it will seal...but for how long?, with the engine running at temperature and full oil pressure. Of course at that point in time the engine will be in the car.

I will try to press it in a little more and take it from there. How much room do I have before I hit the camshaft? Speaking of which...What holds the camshaft in position? As I recall I slid it in, attached the sprocket and chain and thats it. Is the chain the only thing that keeps the shaft from wondering?