Well... the '98+ W-body pieces can
fit... but it takes a lot of work. I'm still getting all the stuff together. You need custom control arms, W-body struts, W-boy ball joints, and maybe even custom axles.
However, swapping in a hub carrier from an A-body with HD brakes and 4 speed auto is plug-and-play. This is a bolt in swap for the Fiero hub carrier. The A-body outer CV's spline onto the manual transmission Fiero axles. The HD A-body hardware also has the 5x115 pattern.
'87 Fiero GT: Northstar, Getrag, TGP wheels, rear sway bar, rod end links, bushings, etc.
'90 Pontiac 6000 SE AWD: Leaking ABS unit fixed, load levelling rear suspension fixed, still slow