There are really no size standards for panel mount VHF radios, even within a brand. Models were much larger ten to fifteen years ago and so an adapter is often needed to fit a new radio. I use 1/4" starboard, 316 stainless machine screws, 316 stainless nylock nuts and 316 stainless washers to fabricate and mount the adapters. Stainless on stainless should be coated with anti-seize so that the fasteners don't gall and lock together permanently. I like the Loctite 37617 Silver-Grade stick for this, it's like a big chapstick. Regular anti-seize is wet and greasy and gets everywhere, some types even burn your skin.
A good basic radio is the Icom 324G which includes a GPS receiver. It displays the GPS coordinates on screen so you can read them out loud when making a transmission and it also includes them automatically when you press the distress button. It will also let you disable the internal GPS if you later add an external networked GPS receiver.
This bracket kit securely mounts the 324G when panel mounted.
Here are a couple of 324G installations using custom fabricated adapters: