From an old hot rodder;
I got tired of no parts listed for 2.5l's or everyone saying that 1" would work. I fabed the first one of wood(black walnut 7/8") and poped it on. worked great some instant improvement. one works, why not 2? even better!! tried 3 but ran out of room with the brake booster. went back and fabed up a spacer of exhaust tube abd 10 ga flanges. raised the throtle cable up an incn and it works great.
while I was at it I opened the intake manifold to the t.b. gasket demensions. get in, buckle up, and hang on!