I can answer somne of these. No, it's not an Apache. I beleive GMC still referred to theirs as "Blue Chip". I have some original literature on GMC from the era, I'll check it for you.
Being a longbed, it could be either a 1/2 or 3/4 ton. 1/2 ton GMCs were the "100" sereis, 3/4 tons were "150".
Dashboards were different between GMC abd Chevrolet, exept for Canadian GMCs, which used Chevy dasboards and engines.
The stabilizer is most likely aftermarket, I've never heard of an OE one.
