Bitter taste of defeat! So much coolant in the oil pan.

1973 Duster 318.
New cam installation and heads gone terribly wrong.

After many hours of cleaning, grinding, chasing every thread, assembling parts, started her up today - took a little fooling with the timing but she finally fired up and sounded good and smooth. Ran the engine at different speeds for about 15 minutes (in the driveway). Set idle, initial timing is advanced about 12-14 degrees. Nothing leaking out of anywhere. Shut it down and let it cool off a little. Seemed like a victory until I got ready to take her out on the road.

Checked the dipstick - milky with some froth and more on the oil cap. Worrying, I pulled the valve covers. Valve covers' insides coated with milky oil. Radiator was down a half gallon. Panicking, I pulled the oil drain plug and lots of pure, green COOLANT came pouring out!

I drained the oil pan all the way and then, to experiment, poured a gallon of water into the radiator. It came out through the oil pan! A good stream, not a dribble, not pouring.

I have made some huge mistake somewhere and would really like some advice/judgement from people who know more than me (just about everyone on this forum).

What I did and how I got here:
Pulled heads and intake manifold
Pulled water pump and timing cover
Jacked up engine, propped motor mounts on big sockets, removed centerlink and dropped oil pan.

Cleaned everything - 40 years of old oil and dirt all over everything and in the pan took some elbow grease but afterward it was nice and clean - gave the oil pan (and all pulleys, timing cover, fuel pump, and water pump) a paint job too.

Put oil pan gaskets on pan including rubber crescents at both ends (used Gasgacinch to glue paper into place, thin line of RTV under rubber end pieces - hate the stupid tabs!)

Reinstalled oil pan, torquing to spec.

Installed fresh-from-the-machine-shop 302 heads with Mr. Gasket thin head gaskets (1121g .028 compressed). Followed instructions on package: "Do not use sealant… gaskets coated with…" Didn't use sealant.
Tightened head bolts in 3 stages in correct order 30 lb/ft, 60, 85

Installed intake manifold (did the same way before: sealant around water holes, Motoseal at front and back). Tightened bolts in correct order and torqued to spec.

Installed timing cover - this was a bear with the oil pan installed. Used RTV at bottom corners and also put some in rubber gasket between timing cover and oil pan.

(Initially, I somehow managed to forget the longer bolt on the lower passenger side that goes into the water jacket - didn't figure it out untll I'd put everything back together again and then, when filling with coolant, saw it pouring out of that hole (which is right behind the water intake pipe on the water pump. Re-installed water pump after putting the bolt in).

All bolts had anti-seize or teflon-laced pipe dope if going into water jacket.

Alternator, power steering, belts, fan, radiator, carb, everything in place.

Healthy doses of oil down the valve pushrods and all over the place, Lucas Break-in Oil and Rotella 10-40 diesel to help ease the cam's break in. Then we get to today - fired her up and everything seemed great. And back to the top of the story.

The plugs look good - I checked them after the horror of coolant. The engine ran good - I would think that if the head gaskets or intake were leaking it wouldn't sound smooth.

I suspect that something went south in the timing cover/water pump installation as the water flowed straight through the water pump and into the oil pan - directly?

So…
WHERE DID I GO WRONG?!?