Brand new here. Just had Whipple install a 3.3L charger on my 496 powered boat. I can't figure out where to install the line for a mechanical boost gauge on the blower. Any help?

Anywhere below the supercharger int he manifold. If there is a plug it will probably be below the intercooler (if present) and in the manifold itself. Follow the bypass valve line to where it goes into the manifold. If a plug can't be located you can tee off the vacuum line that goes to the bypass valve servo.

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"James B." '99LT_Tahoe4Dr2WD, Tuned L29 Vortec 454, 62#Injectors, Cutouts, 4L80-E 10.5"14bolt ,EatonPosi-4.56:1, Gear_Vendors, HydroBoost, (NEXT: Brodix heads, 230/240 cam, SS roller rockers, longtubes, THEN: Intercooled W200R-8psi in the future...)