Diode resistance testing calls for hi/low resistance readings usually with a ratio of 10 or more. It does not necessarily mean one reading will have resistance while the reverse should read infinity, instead it should be hi and low or low and hi. And sometimes, unless you have a comparable readings from another working unit or known resistance stated in the manual it is quite hard to have a definite diagnosis.
The sure best way to test a diode rectifier is through "hot checks". This means with the engine in fast idle (approx 2K rpm), read Vac from the two input wires (usually yellow or yellow/grn) and you should read AC voltages in the range 14~18 volts. Next is to read the output wires (Vdc)which should read above battery voltage, usually 13.5~16 volt DC. You will need to read the battery voltage before starting the motor and the test itself. In this way, you have a reference for the output voltage. If output voltage is equal to or less than initial battery voltage, then the rectifier is faulty. Worse yet, if there is no voltage AC from the two input wires, meaning the stator is faulty or maybe a loose connection.
I believe you have the 150 HP A model with Prestolite system thus your stator has the 7 amp output non-regulated. The radioshack replacement should be a good replacement which costs less than $5. Of course, as PNW mentioned you will need to do slight modifications with the connectors.