replace the freeze plugs while the coolant is down then button everything back up & take it out & run it. if it starts to overheat before you get up to "speed" pull over & let it cool then continue on. How hot is it getting? confirmed with an accurate gauge or there is no doubt that it is running hot? You said you ain't driven it cuz it is overheating at idle, more info, has it always been like this since you acquired it? #1 what do you have for fan (fixed or clutch)/shroud/fan fore/aft spacing. Your pump is good the rad sounds likely (maybe) good, you replaced the stat & I'll assume it is good (& yes you want an 180 or higher). I'd want at least 15 initial (what do you have?). way less likely is a vac leak & block could be crudded up & a person could pull the freeze plugs & car wash wand blast it out (trailer it to/from) but I would definitely not bother cuz if it is OK at speed then the prob is elsewhere. Short version: if the initial is adequate (& I'm assuming that it is) then IMNHO: radiator/air speed/water speed, in that order. EDIT What Savoy64 said, you can get a "tank valve" from O'reillys for less than $3 & screw it into the coolant temp sensor port (1/8" NPT) & pump it up to 10 lbs & see if it holds. With your tire psi gauge in hand hit the fitting with your air chuck for a split second at a time cuz with coolant in there & little dead air space it will reach 10 psi FAST. You can also put a psi gauge on that port & start it & see if it jumps up somewhat high fairly quick which it will if combustion is leaking into the coolant. Those cheap psi gauges are about $5