500 to 700 sounds reasonable to me for testing a well. 3” casing that old is probably and old windmill well. If it tests out OK, you can run a 3” pump on poly pipe by yourself if you want. I think your options of 3” pump include the Grundfos SQ and a pump made by Hydroflo. The Grundfos SQ is not bad when used with a regular pressure tank, pressure switch, and maybe a Cycle Stop Valve. The most problems with that pump occur when it is made into a variable speed pump, which is called an SQE, and used with a CU301 variable speed controller.