That would be the 4L60E transmission.
I have a 1996 305, Vortec with that number on it.
Number one is the front cylinder on the driver side.
is this a vortec engine 4.3 liter casting number on Block 10066061 - 4.3lg
v6 vortec fires 1-6-5-4-3-2 with number 6 5 4 3 2 1 as you're standing in front of the truck looking in the engine
Drivers side front
last cylinder on the passenger side
I have a 95 blazer with a v6 vortec and there are 2 sensor on mine. 1 before the catalitic converter and 1 after it. Both are the same part number. They are easy to replace yourself but anywhere from $46.00 to $79.00 depinding on where you get them from. Good luck.
The Chevy Blazer with a 4.3l engine has a firing order of 1-6-5-4-3-2. The number one cylinder is on the driver side closest to the front of the Blazer.
165432 is firing order I believe the #1 is the lower right if you looking from front of truck
look at the vin# and it will be the 8th digit hope this helps and should be a letter not a number. on my 98' it is a R.