oversized pistons and rings?

hey fellas, rebuilding a 305 and keep hearing something about putting oversized pistons and rings into the thing. how do i know they are going to fit? what is the point of doing this? do i have to do this when rebuilding this thing? what is oversized? do i jus get one size up or what? PLEASE HELP  

Ok when rebuilding a engine if the engine smokes or burns oil and the cylinders are worn then you have to take it to a machine shop and have it bored depending on what it is bored to usually .020,.030,.040,.060 over size then you will know what pistons and rings you need.  
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 sounds expensive, but say i was to take it and get it bored could i still use the stock heads,cam,crank? i would need new pistons, rings?  

It can be  
Professional hi-performance engine builder

Horsepower sells Engines and torque wins races.

Yes the stock heads,cam and crank will still work just have the necessery machine work done like new cam bearings, bored, turn crank, r&r pistons,new freeze plugs, tanked and recondition the rods if it needs it.
Are you building it for power.  
Professional hi-performance engine builder

Horsepower sells Engines and torque wins races.

no, not for power just for reliability untill i can drop in the 496. im looking at a rebuild kit from promar, 300 gets you main,rod and cam bearings, cam, pistons, piston rings, lifters, valve stem seals, freez plugs, oil pump, timing set, gasket set and main seal. im thinking that sounds like the good route to go. hopefully machine shop will be out of the question as well as oversized stuff. all im left with is crank kit for 100 bones, and a tuneup on my edelbrock 650. is there anything else you can think of? i scored a cam for 20 bucks how do i find the GM product number to look it up and figure out the lift duration?  

ok found out the cam i scored is pretty much a stock truck cam, which sucks but w/e now all i need to know is if anyone can think of anything else to do to the 3-0-fried besides the listed above and about how much it would cost to have a carb rebuilt. any help would be greatly appreciated!.!.!  

sounds like you got it covered, just get you a rebuild kit from the local part store the edelbrocks are piece of cake. If you can build an engine the carb wont be a problem. The stock truck cam will be fine for the 305.  

But will the stock truck cam be giving me the most i can get out of this "combo" ive been lookin at some diff cams, not sure what to pick though.  

What is the casting numbers on the 305 heads list them and then I can recomend a cam.  
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Horsepower sells Engines and torque wins races.

i think its 358741 but not sure its under the valve cover i guess? on both sides?  

Yes it is under the valve covers.  
Professional hi-performance engine builder

Horsepower sells Engines and torque wins races.

Ok it looks like 471518 could be 471519 or 47151S theres was 3 numbers under that but i couldnt read them looks like E00 or something.  

Ok the casting has to be 471513 and has 1.72/1.50 valves with those small valves you will not see a noticeable increase in power by going to a larger cam I would use the truck cam if I remember right from what I read on the other site it has a .390/.410 lift right.  
Professional hi-performance engine builder

Horsepower sells Engines and torque wins races.

This is a GM 327 / 350 HP Cam
Intake Lift = .390
Exhaust Lift = .410
Intake Duration = 310
Exhaust Duration = 320
LSA = 114
Rocker Ratio = 1.50
RPM Range: 2200-5200
Hydraulic Lifter

Part Number = 3896929
Casting Number = 3896930

im still looking for some cheap heads... do i jus need to look for some good 305 heads or......