You can use an inline filler for the radiator. Lots of the Factory Five guys use them. I think you can also adapt a degas tank made for small blocks. It fits 351W and maybe 302 but I'm not sure about that one. Finish Line also sells that tank.
On the frame, what you've done looks pretty good to me but I would suggest and "X" brace in the frame. It'll make it more ridged and give you a trans mount. Here's a photo of my frame and you can see the brace in the center:
Larry