any good radiator shop should be able to get you the petcock with a seal that you need, ( Car Quest should be able to get it if you have one, Napa * might * still be able to )
Get one of those prestone flush and fill kits that splice into the heater hose and attach to a garden hose to flush out the system. Use a flush that is soap based not acid based to clean out the system ( main ingredient will be srufactant ) then after running it, flush out with hose through flush tee with all petcocks open till everything runs clean.
DO NOT run an ELC, this stands for Extended Life Coolant, I.E. Dexcool, and it will eat up your radiator and cause all kinds of problems you do not want..
If you want to run a standard coolant go with the fleetguard type precharged to save trouble
BUT, I too would strongly recommend using Evans waterless coolant. Ive been running that stuff in everything I own for years. It may cost a bundle to put in, but with a 375 deg non pressurized boiling point, it is really cheap insurance. No other coolant will give you the kind of margin of safety that you have with Evans. other coolants if something goes wrong, you have just enough boil protection to start aiming for the shoulder and watch the steam start rolling out from under the hood, because its all over but the praying that major damage hasnt already happened, but with Evans, it's almost a joke how long you can run with the temp gauge needle pegged and not hurt a thing, plus you no longer have to worry about SCAs, and in the long run, the cost balances out because you dont have to change it yearly ( not a bad idea to run a filter with it to catch the block residue that flakes off over time as a remnant of years of previous water based coolant use)
