Don't really know anything about inside of engine. I did run my new inspection camera down the #3 intake port and I could see intake gasket and/or face of head port sticking out slightly on 3 sides of the intake port so there is another issue. I'm guessing no on head porting. And I'm learning a lot about racing type parts on a street engine. It has an Edelbrock RPM/Airgap intake and a Holley 4779 750cfm mechanical secondary, double pumper. Also an MSD billet mechanical advance distributor. When I took the carb off, gas was standing in the ribs in the intake floor. So cold intake and big lopey cam creating less vacuum maybe not keeping gas vaporized.
Thread engagement for ferrous is 1.5 × bolt diameter. In Al, I would go 2 × to 2.5 ×.Copied from Fastenal website: https://www.fastenal.com/fast/services-and-solutions/engineering/screw-thread-design
"It appears that one could theoretically increase the thread strength by increasing the length of engagement. However, as illustrated in the Load Distribution chart above, the first thread will be taking the majority of the applied load. For carbon steel fasteners (including tapped holes) the length of engagement would be limited to approximately one nominal diameter (approximately 1-1/2 times the diameter for aluminum). After that, there is no appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it will fail and subsequently cause the remaining threads to fail in succession."