Returning owner, 91 Previa , 93 previa coolant and oil mixed..

Hello Everyone,
I am a van camping fan..
I am on my third (or fourth) Previa..

1st/2nd previa was totalled a few years ago by a decommissioned ambulance..
About a year and a half ago Stan 91 (the bhaigan express) was my daughters van and ran until it dropped the driveshaft (at the rear bearing flange)..
Shaft intact, rearend appears intact
But of course the rear wheels don't roll.. This one got shelved

Recently we acquired an extremely clean 93.
SO after purchasing it I realized the coolant was rusty and my wife took it in for a coolant flushing.
They too about 2 hours on the machine..

About 2 days after the unit overheated about 2 blocks away from my house.
I refilled it drove it home it . It overheated, I topped it up and it overheated and leaked underneath about 6 inches back from the passenger pillar.

When it cooled down. Checked it and it had coolant in the oil..

Before I start replacing the head gasket can anyone detail the freeze plug replacement ..
This van has 180 and Stan has 328.
Should I swap the engine from Stan or just do the heads on the 93?
Also does any one know of a good Previa tech in Atlanta

Thanks

PaddleVan

Atlanta
Georgia

Do you have oil in the coolant?

A lot of white smoke out of the tailpipe, especially at start up?

if you lost enough coolant to overheat out of the freeze plug and into the oil, I'd think your oil would be overfilled a noticeable amount. If it is going into a cylinder or two, it'd be burning off.