My Blitz's

[Lynn Eades]

Some options;
Use an impact driver. Give the head of the screws a hit with a flat faced punch, (square on)having carefully supported the casting at the other end of the screw. This is to jar it free. (do this first) Judiciously use a blunt cold chisel to chase the screw head in an anticlockwise direction. (one well judged blow)
Carefully heat the screws and let them cool. If that doesn"t free them, heat them again, and quench them with water.
One or a combination of the above should free them.

[Bob Carriere]

In similar circumstances....... we use the oxy-acet to heat up the casting to a pale cherry red...... than with a handy dandy impact screw driver start impacting the screw head. The screws can be hard rusted to the point of shearing the flat end of the screw dirver attachements..... but they sell spares.

As mentioned if it does not work at first quench with water....let it sit.... repeat heat process.

Prefer it to drilling heads off 10 to 1.

Another way would be to grind some clean shiny meatl on the screw head and weld a 3/8 nut on the head using the mig welder....... let the nut glow red....wait for the heat to bleed into the casting..... when parlty cool torque gently back and forth until loose.... if nut breaks off weld another one.....

Good luck.

Bob

[Grant Bowker]

The screws holding the back plates onto the pump body are usually staked in place against vibration by using a punch to drive some of the metal from the plate into the slot in the screw from the edge. If they overdid it this could be adding to your trouble. Heat should soften this as well. They might have used loctite or similar against vibration - heat tends to break that bond too.
I can't think of anything in the top corners of a Chev water pump that should be hurt by judiciously applied heat. Don't go so crazy with the torch that you melt the casting but you should be quite safe short of that.
You may be able to get enough heat from a propane torch as used for soldering domestic water pipe fittings but oxy-acetylene lets you put in more BTU/min and keep the heat more where you want it instead of spread so far through the whole casting (and perhaps cooking the lubricant in the bearing), possibly actually using less heat than the lower rate torch.