To through a spanner in the works, my Megan Racing Drift Spec that I bought from the states is 2.5'' all the way through with no restrictions or bottlenecks, looks similar to the Kakimoto Full Mega N1 and I made 265hp with full I/H/E.
The engine has suspected top end work however and will need...
Don't use stainless bolts. Threads are more likely to sieze even in normal applications and they are twice as hard to cut off than regular coated steel.
Basically, I only use stainless in industrial applications where I know they aren't going to be coming back off.