Guys, thanks for all the input on this.

I decided I might as well bite the bullet and tear it down. Upon removing the manifold, I saw a pin hole sized void in the RTV close to the front right corner where the leak was coming from. I don't know if this was an air pocket in the RTV when I applied it or it was caused by oil pressure at the spot. I tend to think it was an air pocket because the engine only had about 4 hours on it since installing. I measured the compressed thickness of the RTV and it was less than 1/8 inch. A 1/4 inch bead of that stuff leaves a lot of room for air pockets and other inconsistencies.

I think I'll go with a combination of the input provided here. I am going to use the cork gaskets applied with contact cement. While they may break down over time, I am hoping it is longer than 4 hours. I am leaning toward using the "Right Stuff" in the corners and maybe a thin film on top of the cork. I've also been told to use a thin film of sealant around the coolant ports on the heads/manifold.

Any other reassembly advice on the top end of an FE motor is greatly appreciated. Thanks again for all the input!