anyone know what a 92 350 mag with roller lifters and a weber
4 barrel carb has for horsepower? is the weber carb anygood?

In 1992 that engine made approx 270 flywheel HP.

would roller rockers and better exhaust "thru-hull & manifolds"
pick up 30 hp? don't want big block cause of the alpha drive
if I had the money Id go alum head & manifolds for the weight
reduction get horse power around 330

Possibly, but for the price you would be better off swapping out for a 454 Mag motor in my opinion.

May cost a bit more but you would have better components plus more cubic inches.

Les