98 Venture Misfire

I have a 98 Venture with 194,000. I'm the second owner; my in-laws bought the vehicle new and I purchased it from them Sept '06 with 181,000 miles on it. I just completed a head gasket job, which included the following replacements / rebuilds in the process:
- Both heads resurfaced, valves ground/lapped, new valve seals/guides
- Head Gaskets, Bolts
- LIM Gasket, Bolts (updated kit, and torqued to GM's new recommendation)
- Fuel injector o-rings and 'sleeves' replaced
- Thermostat, Water Pump
- AC Delco OEM Spark Plugs (it was still running on the originals, and I verified the new ones to the originals by part #)
- AC Delco OEM Plug Wires
- Alternator Rebuilt
- Oil Pump Drive o-ring replaced

As many hours as I've put in on this job, I'm sure I've forgotten something here...

Anyway, to the matter at hand. Started her up last night, and I have a flashing Service Engine Soon light, and it's throwing P0300. The idle is consistent, but rough (not much up and down in idle speed, but there's a DEFINITE miss). The miss persists as I accelerate up to highway speed. Van dies when I tax the engine at all (example: cutting the wheels sharply at low speed).

The background for the head gasket project is this: temp gauge acting funny - showing overheat before the thermostat would even open, needle all over the place from bottom of normal op range to the red, etc. Then, when I started it one evening to take to a reputable local dealer for diagnosis, engine was missing, SES light flashing, tremendous amount of white smoke billowing from the tailpipe.

Does anyone have any recommendations for what the most likely culprit could be? I've been told by a few friends that when coolant was pouring into my #1 cylinder due to the bad head gasket, a healthy amount of it (well, UNHEALTHY really) was passing right into the exhaust, thereby possibly killing either or both of my O2 sensors, as well as my catalytic converter. Does this sound plausible?

I'm desperate for answers here, as I've put nearly $600 total into this project and still don't have the van in driveable condition. Help, fellow Venture owners!
Thank you so much in advance for any help you can provide.

Occam's Razor, folks. All three plug wires for Bank 2 were installed at incorrect locations on the coil. All I can do is just chalk that up to late nights in the shop and a temporary loss of focus...

After correcting the plug wire situation, she fired up and ran like new. SES light stopped flashing immediately. SES light remained steady on, but after erasing the P0300 code with my reader, the light stayed off. Probably the best news of all, considering this was a head gasket fix: temperature is staying right where it should. Despite my bleeding the coolant system per the manual, the temp gauge needle is 'floating' a little, but not nearly like when the head gasket was gone (bottom of operating range, to red, back to bottom of op range, within no more than 30 seconds at times). I'm hoping that any small amount of air remaining in the system will work itself out through the coolant reservoir (seems to make sense that, as long as air isn't constantly contaminating the cooling system like when my head gasket was bad, that the air should make its way to the reservoir and out). This appears to be the case, as the 'floating' of the temp needle lessened as the first test drive progressed.

After completing a pretty major repair on this beast, I'd like to let the forum know that I'll be glad to field any questions related to the head gasket job, and I will answer them to the best of my ability.

Take care, and thank you to all who have contributed so much valuable input to this forum.