Still debating if I should install headers ? I have a stock 350/300 motor with a mild cam. Will I notice a slight hp gain and sound ? Long or short tube headers ? Which Hooker headers do you recommend for my motor ?

I don't claim much expertise, but I've been looking into this for a while during the time I've spent getting my '80 L82 back on the road after a 13 year hiatus. At this point I'm not looking at the question of long or short tubes, but instead thinking seriously about Tri-Y style headers. The L82 engine option's stock cam is a mild street profile which shifted the torque an HP band up about 1000 RPM from the standard L48 engine. Specifically the L48 peaked at around 4,200 RPM and the L82 peaked at 5,200 RPM. Engines which have peak hp up to around 5,500 RPM tend to benefit from the tri-y design. The reason is that mild cams tend to gain most of the hp by shifting the torque curve up in the high RPM range. But in doing so they end up requiring the engine to get to a higher RPM before getting into the power band (something you may not notice much with a 3.55 rear end but which is painfully obvious with a 1980's 3.08 read end). The tri-y's are specifically designed to improve exhaust efficiency and thus torque at the lower RPM range.