FYI , TBI is EFI . I think you mean MPFI which is multi port direct injection like the magnum engines have. The TBI is a throttle body with injectors in TB. TBI is wet manifold MPFI is dry. TBI has all the disadvantages of a carb like fuel suspension and manifold design where as MPFi only has to move air through manifold making it work much better. The factory TBI system is pretty much considered no performance problematic junk. They had issues when new so I would imagine after almost 30 years it would be a giant pita to get it working in stock form much less with a modified cam etc.
I would go with a small afb or go directly to magnum MPFI engine. TBI=not worth the hassle
