I skimmed thru your thread and just like to say it had to be your fault sorry to say.
When a engine has been cold for so long starting it up once in a while wont do a thing.
You prob started it up and only let it run for a minute or less idle then just started driving. You forget the pistons and chambers take time to heat up when it has been cold for so long and starting it up randomly and then sitting for another week without idleing is bad for that engine.
You do know that blazer can fit a gmc sierra or chevy silverado/s10 engine or even a jimmy engine.
When you say old i guess you had a 4.3l engine so its VERY hard to say you cant find another engine for under 400$