Tare it down to the short block. Replace the rod bearings. I would recommend replacing the lower main bearings shells with the upper grooved halves, this will give you full time oiling to the rods. Take a look at the damper. Is the outer ring sitting cocked, the rubber bulging or cracked ? If so get a new one. This should have your short block in fighting shape. I'd call Hughes on a cam, make sure they know the motor is using the EO pistons as P to V clearance will be an issue. You should be able to retain the OE hyd roller setup. I'd think a cam in the 228-232 @ .050 on a 108 LSA advanced about 3 or 4 degrees would be the ticket. As far as heads, I think a set of worked over EQ or Hughes Iron Rams with the LA intake bolt pattern would do nicely without putting a major dent in the wallet. Top it off with a RPM Air Gap intake and a 750 double pumper carb. Headers comes down to budget. TTI would be my top choice due to quality, fit, and power. They are spendy though. A set of Hooker or Hedman entry level units come in at less than half the price of the TTI, but are not as good. Other things you'll need are a pass car oil pan and pickup, Magnum flexplate to correct for the external balance, and distributor. What will this motor make as far as HP ? Depends a lot on how good the heads are done and the condition of the rings. I'd think 430-450 ballpark. Trying to get 500 HP out of what is essentially a junk yard build using OE pistons and stock rod bolts can be sketchy. Keep the RPM around 6000 or less and it'll have a good life span.
