In the tech manual, it lists the NSN for the 6.2 and 6.5 thermostat as well as a P/N (part number) for each.
I discovered that the part number is the actual AC Delco (OEM) part number and was able to order the thermostat on Amazon for $11.00 Free, next-day delivery.
Mine arrive in an AC Delco box.
In fact, here ya go straight from the -280-24P-1: 1 PAOZZ 6620011468006 7X677
14077122 THERMOSTAT,FLOW CON 6.2.LITER......
The P/N is the 14077122. Google that and enjoy the possibilities.
Summit Racing:
https://www.summitracing.com/parts/ado-132-55/
This thermostat does look physically different from the 6.5L engine:
Free Shipping - ACDelco GM Genuine Parts Engine Coolant Thermostats with qualifying orders of $109. Shop Thermostats, Mechanical at Summit Racing.
www.summitracing.com
Why am I going to all the trouble to post this? Because nothing makes me angrier than seeing aftermarket vendors charging $50-ish + shipping for an $8.00-$11.00 OEM part with free shipping.