The L98 is a not so good plan for a 350 without some serious porting....period these heads came with relatively small ports... you may see some low end torque boosted but I'll probably bet this thing fall flat at anything over 4,500rpm.... but you did not say weather you have the cast iron or aluminum version....

If you have the cast iron version (which came on 305's) they are some what of a restriction in non ported form and the engine can actually suffer instead of gain....

The problem is even more aggrevated by placement of a bigger cam....

As for horses if your pushing 295-300 for a factor emissions vette your doing good....