"i would like to get the engine up to 250hp any suggestions."
Headers, free flowing exhaust, free flowing air filter / cold air kit, switch to an electric fan, underdrive pulley kit. You can't get too carried away with these engines, as it tends to stress out the computer. Don't forget a basic tune up when you get it back together, plugs, wires, dist cap, rotor, pcv valve , oxygen sensor. Don't forget to clean the throttle body and IAC valve.
"would a .20 or .30 overbore give me more power and how much hp?"
Technicially it will, but it won't be very noticiable.
"would a cam help and how much power can i expect ? "
It will help, but if you go too big as I said above, it will stress out the computer and you will loose low RPM power. I would call your favorite cam manufacturer, give them your truck's spec's and see what they suggest.
"the motor has 270k miles should i replace the rods?"
I would take them to the machine shop and ask them to check to see if they're bent or cracked. They will probably resize the big ends to make them perfectly round again. Usually, they're pretty durable.
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