Okay, starting to look into engine mods:

First question LB9 TPI in a 91:

Fits any roller block 86 and up ?
Can it fit engine blocks 85 and down?
Will it fit "vortec" heads?

 

As far as I know Vortec heads will work on any '55 and up block, however you'll need a new intake manifold unless you get some of the heads that feature dual bolt pattern.

 

Vortec heads with dual pattern won't help, because the factory TPI base isn't tall enough to cover the ports. If you go with Vortec heads, get a proper Vortec base.

'86 blocks weren't roller. They were one-piece rear main seal, though.

Roller block doesn't have anything to do with how the TPI fit. It's the heads that matter. '87-up have the center two bolt holes on each side at 72 degrees instead of the 90 degrees of the others. '85-'86 TPI, and all Vette TPI, had all at 90 degrees. '86-1/2 & up Vette had aluminum heads with no exhaust crossover passages and with an external tube to bring exhaust gases from the exhaust manifold to the base for the EGR function.

Of course, there also isn't a direct tie between "fit" and "function". But, that's more detail than needed at this point.