When the stock seat is cut out is it normal to slightly get into a water jacket? How would you keep it from leaking were the new seat mates flat against the new flat surface?

Nope, not normal - that's why it's risky to put hardened seats in older heads, especially if they have 2.02/1.60 valves. Time to start looking for another replacement head. :(

Its a very rare head with alot of money in it already. Can the seat be furnace brazed around the lower perimeter?

Only proper way to fix it is to spray weld the whole thing and cut the seat into the new metal. Forget about installing hard seats. They really are not needed 90% of the time anyway.

Just my opinion,

Sounds like a good opinion. Thanks

I have a friend who has his own head specialist shop...asked him about this...
His expression said it all :noway:
Hes never come across it....get a new machinist......

This is a ford 351 cleveland australian head, not a chevy head. I think this has happened before. Howver, your advice on the machinist is not a bad idea.

When choosing a machinist, espec in a larger company where there are several, meet the guy on the factory floorwho is going to do your work ...
And dont let 1st impressions fool u...
The guy who done the maching on my block, talking to him, 'if he had 1/2 a brain , he would die of confusion'
But put him on a mill, boring machine, or balancing, and hes an artist...
Its like is whole world is centered on machining to the utmost perfection.
I supose thats why hes still on the factory floor, and does all the high end specialist stuff.

I took it to a head speciality shop and Dallas and heres what they say. Its not uncommon to cut into a porosity hole when cutting for larger valve (which was my case). No fault of the machinist. They said the head could be saved by screwing a tiny pipe screw into the hole and then machining it flush for the replacement seat. Then they run ceramic through the water jackets to further guarantee no leaks. All this at a cost of 85 dollars. Not bad.