305 Intake manifold bolt question - open to oil?

[OldGray]

I have read where the middle bolt holes on a 350 intake manifold go all the way through the head.  Does anyone know if they do on a 305?

I had a small oil leak near one once and a dab of RTV on the end of the bolt fixed it, so I am guessing the middle ones go all the way through.

Anybody know?  I am hoping to use it (with a hollow bolt) for a bypass oil filter return.  Here is where I got the info:

http://www.wonders-in-wood.us/images/frantz/86install/frantzinstall.htm

[bd]

The intake manifold center bolt holes penetrate through the cylinder head flange into the lifter valley.

[OldGray]

Ok - so I should be good with running a low-pressure oil return there?

[bd]

Not if that means sacrificing clamping force on the manifold flange.  In addition, the exhaust crossover port is between those two bolts.  There is risk of gradually coking oil in the fitting.

[OldGray]

There is a hollow bolt made for this specific application (http://www.frantzoil.com/catalog/item/4746217/8845157.htm).  It gets torqued down and the oil return fitting threads into it. 

Thanks!