A 637 is a GMC V-8 Gas. It looks like a 478 V-6 with 2 extra cylinders on it. Altho the 478 is a slow revving Torquer and the 637 is a faster revving engine in comparison. I used to drive a '71 GMC 637 with a 10-Speed Road Ranger and it revved like a Detroit.
Check with your DMV on the Air Brakes. Is the truck under 26001? Will you be registering it as an antique? I have heard of different rules for different states.
$1800 sounds like a reasonable bid to me.
Keep us posted.
Bill
