How strong is the top bar. If i was to cut the bottom rail of the subframe would the top rail be enough on it's own>?

I'm sure it would be fine as long as you don't ride it.

I saw fry did a complete replacement. I'm thinking of just using the existing top rail with a 45 support rail. Do you think the top rail will be strong enough or a complete replacement similar to fry?

http://gstwins.com/gsboard/index.php?topic=42183.0