Airboxes are off with the bolts. What else secures the TB to the manifold besides the four bolts?
Two Allen head bolts.
Where might they be?
They are recessed from the surface that the air filter housing attaches to, on each side of throttle bore. Maybe a mirror to see them…you should be able to see where they are by the gasket between the TB and the air filter base, gasket won’t be compressed because of the recess. I am assuming V12?