Brought this home today- GMC via GMC

[Vintage Windmills]

Looked at this last sunday for parts. Mainly to use the wheels/tires and hitch on my 71 C20. Price was right since he was going to remove the 454. Well he got the engine out on thursday and the weather was pretty nice today (7 degrees but calm and not snowing) so i borrowed a nice GMC crew and rented a trailer. Anyways, it has some nice options and no rust holes or soft spots anywhere on the box that I can see. Front end was supposedly rebuilt and the truck ran great and everything worked. After looking at it some more, I'm having thoughts of putting back on the road- am i crazy? Tabs are current and title is clean.

I really need some opinions on the cab from you guys who have seen alot more of these than i have- it looks good on visor area outside but has holes inside (see photo) Also, needs rockers, corners, floor patch behind seat and maybe a support or two. There is rust through above engine on firewall. Is this a wierd area to rust? Is this cab too far gone?

Pretty clean underneath with just surface rust on chassis. Truck was originally a southern SD truck. They use little or no salt there. Look at the white on the trailer- isn't the salt up here in MN disgusting? That is why my truck is in the shed until the first good cleansing rain.