I say go for it. You've already bought the parts to build it except for the rear girdle. I remember years back seeing pics on here where someone used a chevelle 12 bolt and used the "ears" and custom uppers (with rod ends I think) so it was triangulated. I seem to recall they were long uppers that mounted low near the LCA to frame mounts. I don't think it used a panhard bar anymore. It wasn't one of the newer (at the time) builds, but was pictures of an old race car if I remember correctly. I saved them, but that was 2 or 3 computers ago at least.
I've seen (and done it myself) people give a lot of hell to the little 7.5" & 7.625" ten bolts in LT1/LS1 cars. They usually hold up until they are running in the 12's with an automatic with drag radials....and even for awhile with the six speed. They will bust with the six speed and drag radials when the motors are stock.
I agree the 8.5" would have been better, but you will still be a step above our 8.2" - 17 spline pumpkin rear in my opinion. Almost forgot, I had a 64 Chevelle SS with a very mild 454, M22, and an 8.2 posi ten bolt....3.73's. It was a factory 283/4 speed/12 bolt car. The original 12 bolt had been scavenged before I got the car. I never had slicks on it, but the guy I bought it from gave it royal hell on the street for a few years while I drooled over it. Finally got it (along with many problems (not the rear) after his abusing it....and swapped it for a 1962 Bel Air 2 dr sedan 6cyl/3 spd which is now collecting rust.