I've heard the L98 aluminum heads on the 350 Tuned Port are a direct bolt on replacement for the cast iron heads on my 305. Has anyone done this swap? Did it help substantially. Not looking at making it a screamer, but would like to know some bolt on modifications I could do or a good heads and cam combo. It's the 305 that came from the factory with 230hp.

there are a lot of links on this - hit the search button and watch the screen fill up.
there are some problems with the vette heads. first and most important is that there is no egr bypass for it. no hole that connects it to your tbi or tpi. you need to make one. its not hard but if you get a bad smog referee he will know immediately that its not stock and your egr valve will not match the numbers that same on your car as oem.
but if you dont care about smog then they are fine.
be sure to do the search -

You will need to get vette tpi intake or eldelbrock one with the vette type egr passage that hooks to #8 header pipe if you need to run egr.
They work great on 305.

The state I am in doesn't do emissions testing so passing smog isn't a big concern. How much do these heads generally go for?

I've seen them between 250 and 450.
You need to clean up ports before using. They run a lot better with mild porting.
They have a D shaped exhaust port.
I used the vette headers also, so I don't know if the port makes any diff with regular headers.

I seen this http://cgi.ebay.com/ebaymotors/350-3...1%7C240%3A1308 an d was thinking if this would fit i am wanting to get some aluminum heads too for a better look