'84 1/2 ton 2wd, '74 350 interceptor questions

[silverbullet01]

hey guys, i've got a '84 chevy, running a TH350 and 273 rear gear, my motor is a '74 350 police interceptor, im running 882 heads, steel intake, and manifolds. i just put new head gaskets in it and intake the gaskets, the head gasket on the drives side between cylinders 3 and 5 was missing a piece 1/2 an inch big and was skipping and spark knocking. i changed it, and the truck worked great for about 2 days and is now skipping and smoking. a guy told me its probably got a broken ring, what do you think? this winter i have a set of .30 over pop up pistons, a factory GM aluminum dome, and i plan to get a cam and lifter set to put in it, nothing insane, but something with a rough idle. i also plan to switch it to a bull low 4 speed, any one have any ideas what it would make for horse power?