Those HT383s are great motors, from what I hear. I recently read an article in Chevy High Performance where they went and modded an HT383. They swapped in a Comp Cams Xtreme Energy #282 hydraulic roller cam, an Edelbrock RPM Air-Gap Vortec intake, some slight headwork for the pushrod guides and valvesprings, GMPP 1.6:1 rockers, and a Barry Grant 750 cfm Speed Demon carb, and boy they did good. It made about 449 bhp @ 5300 rpm and 486 lb-ft @ 4200 rpm. It also made over 400 lb-ft of torque from at bit above 2000 rpm all the way to 5800 rpm!!