They will send your part request along with your email address to salvage yards all over the country. Any salvage yard that has your part will contact you via email with price and shipping information, etc.
I have used them several times. I got a transfer case and a heater blower assembly for my '86 F-150. I have never received any spam as a result of my having used the service.
I think it would be better to purchase/replace both heads. If any Machine work has been done different on one head it could cause problems....Just a thought.