I have the Y303 heads and the stock pushrods work. But, I do have some rocker noise coming from the valvetrain now. From idle to about 1800rpm it clatters/ticks and is only noticable by me when I am sitting next to a car or wall in traffic. Too loose? I think I could go up to a 6.300" pushrod. Stock pushrod length is 6.272".
Being that the stock E7TEs' are a 58cc chamber like the X305 heads I think you will probably be okay. Unless you have a Cobra with cast iron GT40 heads with a 65cc chamber. Cobra engines, I believe, use the same 6.272" pushrods. If anything they will be slightly too long in which you could get the FRPP shim kit for $10 from SummitRacing to raise the rocker arm pedestal. That is the cheaper way to adjust the bolt-down rocker arms. If they are too short the shims will not help. The other alternative is to buy roller rockers with adjustable pushrod cups. The way I am looking at it though is the price for new pushrods ($90 from SummitRacing) + the price of 1.7:1 roller rockers is about the same as the Steeda shaft mounted rockers with adjustable pushrod cups.
I do know that the instructions for my Y303s included the X303 and X305 heads as well. They don't mention a need to get different pushrods or rocker arms.
A lot of people here were saying that the Y303s aren't worth it because they don't flow like the TFS TWs or AFR165s. I like them and the price was right. I gained .4 sec at the 1/4mile which is on par with the 10 horsepower per .1sec rule. The Y303 heads are supposed to be a bolt on 40 horsepower. That said the X305s are not going to be too much head for a stock 302 engine.