New or rework?

[Phillyfanfrombirth]

Whatever you do, don't go too big if your pistons aren't cut and you have a high lift cam... and be sure to have hardened valve seats that don't require leaded gas.

I have a set of Windsor Jr. heads that did a good job, but they were really a pain to get a set of headers (this was on a Maverick) on without busting up the plugs, I had to use a set of shorty plugs, and couldn't change the plugs without unbolting the headers... I also ended up burning through the plug wires more than a couple times.

I didn't have the same problems with the stock heads, so I'm sure something was angled differently. That was about 10 years ago, so they may have changed something... and headers made for a Mustang may not have the same problem that I had.