4.3 bored over
 

im just wondering but how much would it cost to bored a 4.3 over? And how much more horsepower and torque?

generally "boring " is to fix the hole
If its out of round or scored the more it needs
When I see guys quoting big numbers I think that was really ef'd up block they started with
IMO your not going to make any gains with boring
Once you bore it you need to put in new pistons and rings to match the hole size

some things to increase HP are Port and polish heads, decking the block ,matching intake, gaskets and ports
BTW HP costs money

If you google "how to increase HP" you get some other ways but beware some are snake oil
Short of Dyno testing it really hard to determine other than seat of the pants

On my 1st gen I think it was about $800 (but might of been $600, it was over 10 years ago) to rebuild the 4.3 short block. I had to remove and bring it to them. Like Rex said, you dont really bore to make power, you bore to fix. If you aren't burning oil and dont smell gas in your oil then you probably dont need to bore out your engine.

you will gain something boring an engine out. will you notice it??? probably not, unless you dyno it. but, since you have bored it, you will also hone it. by they time that you are done honing, you will then have increased the percentage at which the rings in the pistons seal to the cylinder wall. that is where you will make some power. you will have less blow-by and better compression because the better seal isnt letting so much out. but like REX said above, you will make most of your gains in head work and port work.
think of an engine as an air pump. the faster you can get air in and out, the better it will work. a good valve job can go a long way. and if im not mistaken, you should be able to put bigger valves in stock 4.3l heads.

just my .02