If you can't get it from underneath, which would seem quite difficult, I'd definitely try what Tony shows there. That method appears in numerous TR Websites. Be sure not to blow any fuses or to short the battery terminals. You might first disconnect the ammeter gauge wires.
It sounds like something is jaming the latch arm. You know there is a small nub on the other side that might be jammed, too.
I like the idea of someone putting a towel or blanket on the bonnet, and then pushing down, maybe pulsating a bit over the latch pin like CPR, while you pull those cables.
I'd be very patient, consume a few beers, and tell yourself it will be all afternoon and maybe then some.