1985 chevy Blazer cranks up, runs rough, then

If you went off the road and the snow jammed into the engine compartment look for something bent and striking when the engine is on. If you find nothing bent or broken and the noise is coming from inside the engine you may have a bent valve or connecting rod. When an engine is abruptly stopped thing can get damaged. Take a wood shaft like a broom handle and place it near the bottom of the engine when running on the block and place you hand on the end of it and then place your ear on your hand and lesion for a knock. If in the bottom could be a bent connecting rod or also called a piston rod. If noise is in the top more likely and bent valve and the engine may run rough. If you not sure have a mechanic lesion to it. You can consult your repair manual for further test. Good luck.

valve cup not holding oil?

looks to me you have flywheel crack or bolts flywheel and torque converter end play

The (engine vacuum) routing-- is on the radiator support label
under the hood support rod

you dont have a choice on a tranny with a 2.8 v6 my suggestion is to go small block chevy if you have the money.

All GM have ignition coil problems , your getting too much fuel , I have seen O2 sensors and plugged catalytic mufflers too many times , be careful the next ride the vehicle will catch on fire..Try the coil first

Possibly the switch at the bottom of the steering column, that the rod pulls on. May be loose, or worn out.

you can usually find all the parts your needing parts and labor for tie rods, ball joints, control arms springs shocks idler arms pitman arms parts and labor will probably run you close to 1500 dollars probably lower.

gas tank

Check your electonic ignition swith under dash that the ignition acuator rod connects to about $8 part at parts store