Coolant is spewing out of my coolant overflow reservoir. I have replaced the black overflow cap, thermostat, water pump, and new antifreeze (50/50 mix), but it still keep bubbling out. Please advise! I need my Volvo on Monday morning!!!

BACKGROUND:
Late Friday afternoon, I noticed a cloud of white smoke coming from my tailpipe while driving at highway speed. A minute later, I noticed the temp guage was in the the RED ZONE. I was near the local Volvo dealership, so I pulled into the shop (5 minutes total). By the time I got there, radiator fluid was boiling out from from the coolant overflow cap. The Volvo service manager suggested that we replace the thermostat and get a new overflow reservoir cap as a first step. However, they were booked up and cannot work on my brick until Monday. I let the car cool off, they gave me a gallon jug of water, said "Good Luck", and I headed home. I drove non-stop with the heater on max at 40-60mph for 15 minutes. (STUPID! STUPID! STUPID!) A block from my driveway, the engine died. I let it cool for a minute, started back up (roughly), drove another 30 seconds home, and parked it.

REPLACED TODAY:
- Radiator Overflow Cap - Volvo service manager said the cap is no good once it has been "popped"; new black cap from dealer.
- Thermostat - old thermostat was broken on top; replaced with Volvo/Wahler brand from dealer.
- Water Pump - possibly the original pump, not replaced in +60k miles; replaced with GMB brand from local NAPA parts store.

THE PROBLEM:
Now when I crank it, the engine idles roughly for the first 10-20 seconds. With coolant level on "MIN", it takes 2-3 minutes for the level to rise past "MAX", then it starts spewing out again. But there is no oil on the dipstick that I can see.

What is the cause? Did I ruin a second coolant cap when the fluid spewed back out? Is the (original) radiator in need of a good flushing? Have I blown the cylinder head gasket? (white smoke from exhaust) If a 240 cylinder head is warped, would the B230F engine still crank?

Why would a blown cylinder gasket cause the radiator fluid to overflow, anyway?

Please advise asap. Tell me I overlooked something cheap and easy...

[[ southern fried volvo '91 240 132k mi - fried engine? ]]