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 Pickup - Imelda
'08 Tacoma TRD
'09 Kawasaki KLR650
'12 Gunnar Rockhound 29
"To live is to suffer, to survive is to find some meaning in the suffering." -- Friedrich Nietzsche