Vic, I was running 43% on my 468 motor and ran 7.50's. My blower is quite worn and probably could use a rebuild, or at the least, new stripping.
I would strongly suggest you get ahold of SFI and get the spec sheets for what chassis cert you want. I'm guessing you will want the 10.1E spec witch is good for advanced ET to 6.00. I git mine in Nov. of 2005 and it was $37.00 including shipping and handling.
http://www.sfifoundation.com/
The one area I would be concerned about is the diagonal from the rear end upright. I see you have a single bar there. Although that is OK for the SFI, once you start making power it will give you problems.
Somes friends of mine had a car like that and Murf McKinney told them what I just said and they actually broke the rear end housing on their car. They had it changed, not sure if they went to a K or an X design, but they didn't have any more problems with it.
Good luck with it.