If i remove the front fender on my 72, do i need to install a brace to replace it or is it OK to run it without anything there? I haven't had a bike with a metal front fender before, and just wondered....

 

The fender does not really provide much of a brace for the forks. You can take it off pretty much with impunity; however, remember that stones, pebbles, sand, and water will be flying up at you.

 

I took mine off for a while and it felt exactly the same so I don't think there is much structural to it.
After running thru a couple wet spots on the road from peoples sprinklers and getting a face full of water I put it back on.
If you do decide to permanently remove it make sure you grind off the attachment points on the fork tubes, just looks so stupid with them still there with nothing attached IMHO.