From the notch, contour around to Allison Creek. The lumpy space makes it challenging to not lose any elevation, but do your best. Skin across Allison Lake, and then curl around the back of 42xx as shown on the overview topo. This puts you at the top of two northwest facing lines, both about 900' vertical, going 42 and 43 degrees, both guarded by cornices. View looking up towards the lines (marked in green) as you approach:

Looking down the second of the two lines:
Alternatively you could boot these lines directly, but the cornices challenge topping out. The skin route goes faster. Be careful dealing with the cornices entering the chutes. Scout the land marks as you pass 42xx' to help drop into the right place.

This view looking to the end of the Allison Creek drainage from the 42xx' approach shows other skinning and skiing options:

Allison Creek Drainage approach overview
Routes Page