Those allow you to align the heads on the block without moving the head gaskets. They also hold the head in place until you get all the bolts started.
So, yes they are necessary.
When disassembling the motor the block had these 2 little round things in them, i'm not even sure what to call them. They are kinds like a small pipe thats 1/2" long but it has a slit down it. You can see them in this pic they are in the top left and right. I assume i need to re-install these? what are they called? I changed from some stock head to the 990's if that matters.
http://reitanfamily.com/gallery/d/5918-2/IM000784.jpg
here's another pic from the side.
http://reitanfamily.com/gallery/d/5948-2/IM000794.jpg
Those allow you to align the heads on the block without moving the head gaskets. They also hold the head in place until you get all the bolts started.
So, yes they are necessary.
No, it does not matter what heads you are going to. From 990s to Pontiac Pro stock heads, they are all cut to take the same size dowel.
YES! They are manditory. That is what locates your heads and holds them in place.
And on to a little different matters, you can get them with slight offsets to move the the direction you wish for a change in valve shrouding or whatever. But for your application, just keep those and go run.
i'm going to need some new ones, whats the stock diam? i was looking on summitracing and i found 2 sets but all with diffrent sizes. Whats stock?
MRG-4377 Mr. Gasket Cylinder Head Dowel Pins
Cylinder Head Dowels, .646 in. Outside Diameter, .503 in. Height, Chevy, Big Block, Pair
Today $9.69
TAV-02810 Tavia Cylinder Head Dowel Pins
Cylinder Head Dowels, .632 in. Outside Diameter, .503 in. Height, Chevy, Big Block, Set of 4
Did you toss your old ones? Many shops give you a set when they machine a block, or at least give you your old ones back. You should be able to pick up a set locally and not slow yourself down.
The first machinest i used only gave me 3 of the 4. I found a set of 4 at napa that matched.
You can get them at the Chev dealer.
Or any speed shop, I've bought them at Napa before!..