Indeed
@Clutch, I bet that one I linked is heavy being all steel. But on a Hilux with 2,000 kg of payload I guess a bloke doesn't gotta worry, eh?
FWIW, a Ute Bed goes about 280 lbs in a Tacoma size, mid length size (6'8" long, 6'0" wide) while the stock bed with (on my 2nd gen anyway) fiberglass inner bed is about 350 I think. Your 1st gen is probably similar. So that's a potential +/- 50 lbs of GVWR recovered and you get half a foot more length and a totally flat floor.
Of course if you do a 500 lbs steel tray that's lost and some. :-( So you gotta be mindful of what you do.