If the cab is solid, with only surface rust,grille is there,sounds like a decent buy.
What would someone pay for a 39-46 cab? Griile?, running boards? etc. And if you do most of the work, That sounds good to me.But of course $500 sounds better. Sounds like you've done some work on other cars.I say go for it and show of some before and after pics.
Perro