I am going to have a huge hole! The valve cover and head stick so far out that I am going to have to keep cutting the hole bigger. The firewall is big and not allowing the clearance I need. I just wanted to make sure I did not cut it out and find later that I could have done something else and made it a nicer fit. This is my rough cut and I will smooth it up later. I have not yet cut out for the muffler. I think I could have gone inverted and had a really clean fit. It is a Saito 80 GK on a Seagull Ultimate.