Another 302 Head Question

Hey all! I'm new to this group but have read through many of your posts. I finally joined, not because I have an A-body, but because you guys seem to be some of the most knowledgeable when it comes to 318s. My vehicle is a '69 D200. 727 trans with 3:54 D60 sure grip out back. When I started the project, my had an engine shop inspect the original motor, it checked perfect so they had a new cam, intake, 4bbl carb, headers, timing chain and the pertronix ignitor installed. Keep in mind, I was 13 at the time. Anyways, this last summer was the first summer for the truck being completed, I put a few miles on 'er to say the least. But the head gaskets appear to be leaking. So I'm pulling the heads sometime the spring so I can have it ready for the summer; i'm away at school for months at a time.
Sorry for the novel, I just like people to have all the info when I ask a question lol.
I was offered a set of 302 heads, no cost to me. I pulled them yesterday and they look to be good. I'm going to get them magnafluxed, and if they are good, I will do some home porting. Free horsepower is never bad, no matter how small. Anyway, i've read and wondered if these castings are thick enough to follow 1wild&crazyguy's thread for porting?
Also, is it worth my while to have the heads milled? Looking to run a thicker head gasket, cause I can't tolerate leaks.
Truck Specs are as follows:
318
Stock internals
Eddy performer intake
QFT 580 cfm carb
Long tube headers
Comp 252H cam (small, I know, but runs real nice in a truck)
3:54 gears
A727
I know naysayers will come with "no gain in 302s" but I can visually see a difference, plus if the heads are coming off I believe there's value in improving what you have. Thanks!