fyi, and fwiw. the stock 460 intake has been quoted as being as good as what was the supposed best ,the offy intake, except for weight.I ran 9;30s in a 6000 lb van with the stock intake and exhaust manifolds.
It was the 1/8 .the van was my dragsters tow car. On test and tune days i would run it. the eng was a .060 over 460 with police interceptor heads ,a rv type cam and a 600 holley,c-6 with a 3.50 posi. Built it out of an abandonded 6 cyl van. eng was lots of extra parts i had. when i sold the eng it was put in a fox and lots of gear first time out it ran low 7s, eng never had nos. they changed the cam and went 6s. 6000lbs down to 3000. thats a blast.
The stock intake has HUGE ports that can move plenty of air for most any street application. Unless you gotta have to looks of an aftermarket intake, save your money for better things. You can get the best results possible from the stock init just by matching the manifold and head ports to the gasket opening. You should make up a 12" section of 3/8" steel cable with a short (1/4") collar secured about 2" from one end. The collar can be wire or tight fitting tubing and it must be brazed or hard soldered to keep it in place. The 2" of cable protruding beyond the collar is separated using pliers to give it a "bloom". Chuck the cable in a drill and the "bloom" end is run into all the manifold runners to dislodge any crud that may be hanging around hidden up in there. Be gentle doing this on an aluminum manifold.