You did properly bleed the cooling system after replacing the elbows, right? If not, then I'd suggest doing that and then go from there. These engines are sensitive to air pockets and can often show low on coolant if there is a bunch of air in the system still. Even if overheated these motors rarely eat HG's.
And if you do pull the heads then you need to get new head bolts as the stock ones are TTY and NOT reuseable.
If you have bleed the system of air properly then I'd follow what PaulieDoggs said and check for exhaust gasses in the coolant.
