I'm adding a Holley electric choke kit (for internal vacuum) to a 4779-6 750 double pumper w/ mechanical secondaries. While there is an opening in the main block that is fairly deep (1.5 inches), I dont think it has access to vacuum. There is a hole going down through the throttle plate but it does not go all the way up to the vacuum port for the choke piston. Its only about 9/16 deep into the main block. Can/should I drill this out so the ports can connect or is there another source to vacuum I'm not seeing. I've added a few pics to illustrate what I'm talking about.

By the way, the Holley Tech line guy said I MUST to use an external vacuum choke kit. I already bought this one from Ebay and opened it so I can't return it. I'd like make it work if I can.