327 intake manifold question

[TheEmrys]

I had posted earlier about switching out the exhaust, but I have found that I have a more important problem: my edelbrock carb isn't seated very well. So, I ordered a new intake manifold to better serve this Elky. And since I got a nice polished one, I figured I might as well get matching valve covers. So, this I have done. So then, I was just hoping someone could give me some sort of an idea what sort of changes I should expect for the car. I know I'll need to do some valve cleaning while I have the covers off, but what difference will a new intake manifold (that mates up flush instead of having an adapter plate required) with the carb.

Here is what I have now: Edelbrock 600cfm, electic choke on the original manifold.

Here is what I am going to have Sunday: Edelbrock 600cfm with an Edelbrock 21011 intake manifold.

Also, I had a guy at autozone try to sell me a $40 (!) gasket for my valve covers. They come with "load balancers." Is there any reason I should go back and trade the $8 piece of cork I bought for the big, thick plastic/rubber monstrocities he tried to sell me?

One final question, should I go ahead and go for breathers? What difference will they make on this car?