Hello!
I must admit, I am somewhat confused as to what parts lisings you are referencing... there appears to be only ONE water pump available for this engine, both in AC-Delco's listings and in NAPA's most up to date internet based parts catalogueing system. No mention is made at all of different pumps with different rotation directions.
The correct part number for an AC-Delco water pump is a 252-825; list price is $123.43.
The correct NAPA part number is a 559342; the alternate NAPA part numbers listed are a 571-526 which is a reman version of the 559342, and a 1652001, which is their cheap chinese line of pumps, but is interchangable with the other two. There is no mention made at all in any of the listings as to a reverse rotation design.
The correct thermostat temperature for this engine is a 195 degree stat; installing a thermostat that opens at a lower temperature is not a recommended practice, as this will cause the engine to run richer than normal (due to a lower than normal Coolant sensor reading). A long term rich condition can cause other problems, such as damage to your catalytic converter.
The symptom you describe (heater blowing cool before teh engine overheats) is indicative of low coolant level in the system. When the coolant level drops below a certain point, there is insufficient liquid available to flow through the heater core, and the first symptom you will notice while driving is loss of heater temperature. It is obviously not a blocked core, or you would NEVER have any heat.
The symptoms you describe are consistent with a head gasket sealing problem, allowing combustion gasses from a cylinder to seep into a cooling jacket. This heats the coolant very quickly, and the gas bubbles displace coolant into the overflow tank resulting in low coolant level in the engine and an evntual overheating condition. Sometimes, such sealing problems only occur at certain engine temperatures (as the block and head expand and contract).
It sounds as if the mechanic that looked at the car did not do a very thorough job in checking for the cause of the overheating problem, and just threw a thermostat at it in hopes that it would fix it. Thermostat operation can be easily tested, either by boiling it in a pot of water with a thermometer and watching to see what temperature it opens at, or by using a scan tool to monitor the engine temperature that the thermostat opens at.
I would suggest taking the car in to a competent, thorough repair facility to have the engine diagnosed correctly. Usually, this involves:
(1) Chemcal test to check for exhaust gas in the cooling system
(2) Cylinder leakdown test to check for head gasket seepage
(3) Cooling system pressure test to check for small leaks
(4) Checking the thermostat operation and cooling fan operation.
I hope this is helpful; if so, an accept would be most appreciated! thanks!