Any idea on what caused the crack?
Does it go all the way through to the outside?
Get a fiberglass repair manual for west system or similar. You'll need to remove all loose material and taper back from the crack then rebuild with patches of glass starting with a piece to initially cover the crack and adding bigger pieces as you layer it in. Probably 3 layers of glass.
1997 2400 SCR
5.7 Vortec / Bravo 2