For the valves, try Woz, I think you'll struggle to do any better...

'The valves are off the shelf stainless items, 45mm and 38.3mm with wasted stems. They are from a company I deal with through work, I can supply them for $28 each+ freight,

Cheers
Woz'

Have a look at the post just bellow 'Pinto build 2' http://classic-ford.org/forum/post.asp?method=Reply&TOPIC_ID=21044&FORUM_ID=7

As for the heads, the most common method is to machine the exhaust seats, and interference fit a hardened seat. They then recut the valve seat. Just google unleaded seat conversion, theres plenty of info.

Shaun