Re: 1967 gmc
 

I can't see why they wouldn't have. Replacing a 305 in a pickup to a larger 351C upon request from a dealer was not to uncommon during that era. GMC did promote repowering all brands of trucks with their V6 engines including their own older trucks, dealers were set up to do conversions.

Re: 1967 gmc
 

Could I plug that hose if I run a breather on the valve cover?

Re: 1967 gmc
 

Your 67 has a closed positive ventilation system, plugging the hose is not a good idea you may build up too much pressure in the crancase system and the valve cover breather without a tube that runs to the air cleaner will not be adequate. It's not that difficult to come up with an attachment to the air cleaner. My 68 does not have the tube that runs from the back breather, I use a K&N open air cleaner setup but I have retained the factory ventilation system which uses a breather cap with tube to the air cleaner, modifcations were relatively simple:upyes: I will post a pic of the setup in another post.

Re: 1967 gmc
 

Guess I need to fix mine. lol Been running just an oil breather and that's about it.

Re: 1967 gmc
 

What you can do is update it to the 68-74 style valve cover breather with tube, eliminate the rear breather/filter and just cap it off with an expansion plug. I'll post a pic of my 68 setup tomorrow when I get home.:ok:

Re: 1967 gmc
 

What type of motor oil do you guys like in the 305?

Re: 1967 gmc
 

I run 15w-40 in mine year round. Seems to be fine. I think Straight 30 is the recommended oil though. Be sure to add some zinc in the oil to keep the cam from being wiped out. I plan to start running ZDDP.

Re: 1967 gmc
 

I too am running 15W-40 in my 478M but using Rotella oil which already has zinc in it:thumbsup:

Re: 1967 gmc
 

30w Valvoline Racing. Lots of zinc.

Re: 1967 gmc
 

You'll find lots of previous posts on this topic in the archives. If you ask 10 different guys, you'll probably get 10 different answers. In my opinion modern engine oils are so much better than what was available 50 years ago, that you can't hardly go wrong with almost any oil now. That being said, a high zinc oil is definitely better than a low zinc one. My favorite is http://www.amsoil.com/shop/by-produc...?code=ZRTQT-EA, also available in a 20W-50.