177mm should have no problem with the 42mm. The biggest thing when it comes to fitting a watch is making sure the watch fits lug-to-lug on your wrist without hanging over the sides (hopefully that makes sense). Here's a comparison, they are are actually pretty similar besides width, which is less important than height IMO.
Apple Watch 38mm
Height: 38.6mm
Width: 33.3mm
Depth: 10.5mm
Apple Watch 42mm
Height: 42.0mm
Width: 35.9mm
Depth: 10.5mm
Pebble
Height: 50.8mm
Width: 33.02mm
Depth 10.16mm
Sounds good the Pebble didn't seem too big for my wrist so I shouldn't have any issues with the Apple Watch then.