Our 96 S10 4.3l was missing and backfiring through the exhaust. Would smooth out some with acceleration.

When you crank it now, is there spark to the plugs? Also is the timing set correctly? Do a compression check and make sure you don't have a blown piston or bad valve. Is the injectors firing at the correct time and are they getting fuel?

There is spark to the plugs. I am pretty sure the timing is correct. The injectors are performing as they should. A compression check sounds like the next step. I guess what has me so puzzled is why gas and all of the oil poured out of the crank case when the crank shaft sensor was removed? The oil doesn't even read on the dipstick now. It seems to be we fix one problem only to run into 3 more. It started with a P0300 Random Misfire code. With several indicators. Not sure if its worth all the $ we keep putting in to it...

A compression check will tell you if you're holding pressure in the cylinders. You, if the readings are low, may have a cracked head, burnt valves, cracked block or a hole in the pistons. A complete tear4 down may be in the works if there are bad readings. A new crate motor would be one possibility. I'd check the timing first before starting an expensive tear down.