383 connecting rods

Nope, not all 383 cranks are forged. The 383 2bbl engine in 1971 used a cast crank. They all had forged rods. The stock forged crank and rods have been used repeatedly to over 7000 rpm. I would recommend you replace the stock rod bolts and resize the rods.

906 head, KB400 piston, 9.5-10:1, doable? If by that you mean, "Is it physically possible?" Yes. A 4.280" bore, 90cc head, zero deck, .040" head gasket will get you 9.5:1.