Here is my 75 hp and torque boost: Start with a set of the new Edelbrock E-Street aluminum cylinder heads. They feature 185cc inlet runners, hardened spring seats, and heli-coiled threaded rocker bosses unlike the low-cost import aluminum cylinder heads. They are offered in two combustion chamber sizes; if you go with the 70cc heads (PN 5073) you'll get a nice 0.5 compression bump over your iron 882s. Match these heads with a Performer RPM PN 7101. The RPM Air-Gap will give you a few more ponies; however, we've run into carburetor icing issues with the Air-Gap. Again, we don't know your intent.
Finally, go with a Comp Cams XE256H camshaft. This is a relatively short cam with 212/218 degrees duration at 0.050-inch tappet lift, 0.447/0.454-inch max lift, ground on 110 centers. These above components will give you at least a 75hp boost over the current package you're running with minimal impact to the driveability to the vehicle.
Finally, stick with your exhaust system for this package. We don't think changing out to the long-tube headers and larger exhaust system will be the difference. The 21/4-inch dual exhaust you currently have will support the 330 crankshaft horsepower we believe you'll be producing.
Sources: compcams.com, edelbrock.com
Technical questions for Kevin McClelland can be sent to him at email@example.com.