Put me in the agree with Christo camp.
I did the whole engine thing, which in the case of a 19 year old Hilux almost doubled what I'd spent on it. So 'upside-down' is sorta relative when the $5K, 90K-old used truck you bought gives you as the second owner another decade and 97K of service. I didn't mind spending the money I'd saved just driving it, in other words.
However, knowing now what I wish I did 5 years ago, I would have done a minimalist rebuild.
These are service and utility trucks, they're not gonna see Concours d'Elegance or collector auctions. Keep 'em running and reliable, no more, no less. I would in your situation just clean it up and put in a HG. I might refresh the head, but that depends on the shape it's in (mine needed it regardless that the timing chain let loose). I would rebuild the short block only if the rings had stopped sealing altogether or it was warped.
'91 Toyota Pickup
'09 Kawasaki KLR650
'12 Gunnar Rockhound 29
“Anyone who believes in indefinite growth in anything physical, on a physically finite planet, is either mad or an economist.” -- Kenneth E. Boulding