Bass build, advice sought about weight

Well I can tell you chambered bodies are not necessarily the lightest, depending on wood used, and the internal rib layout and construction. Some builders would point out that their chambered basses offer different tonal possibilities, and aren’t chambered for weight, but tone.
Edit- hollow bodied basses and chambered basses are different. My lightest bass is a hollow body (violin bass). Those are light!

 

I'm not sure that 4 8 gets you in the 8lb range, but a lot depends on hardware choices. I want to say my J was about a 5 lb or a little heavier, and the finished instrument is 10 on the nose (with an active preamp, which probably adds a little weight.

I think the main places to look would be at the neck and tuners. The warmoth necks with steel bars are pretty heavy. The graphite ones probably save close to a half pound. For tuners, Schallers and schaller styles are beasts. I have a set of tuners from MJT and they are every bit as heavy as the Schaller ones. You can shave something like a half pound off a bass with hipshot ultralights.