Let me add my opinion....since it IS worth so much. :-)
First off, the blazer replacement will force you much work....the 1-3/8" filler
and the fact that if its intended for a fleetside bed, major modification of the underbed support rail.
The ECE version may seem pricey in the beginning, but...in the end you will be happy with it. 2" filler tube (at least for a side fill set up) Bolt right in using the stock holes (if a short bed will require removal of the original frame cross member, and the include a nicely made replacement) You can also specify carb or fuel injection (my recommendation, get the fuel injection version....it can be used with a carb and gives you the option of upgrading later) Comes with a 0-90ohm fuel level sending unit made by VDO. Holds 22~23 gallons. Made out of stainless, so it wont rust.
Here are a couple of pics I have of my install. Only thing I requested on the tank is a 1/2" NPT bung installed apprx 2" in front of the side fill port, for the vent during refueling to prevent backfill issues. (this is non-standard to the ECE, special request) The filler door is from an S-10, not sure of the year.
here are a coulpe of links (since I cant figure out how to add pics anymore)
http://www.prismnet.com/~grzanich/ECE_FuelTank.JPG
http://www.prismnet.com/~grzanich/71...iller_door.jpg
Will be glad to answer any questions in regards to this.