My wahoo gun is a Koah bluewater 65, I have been trying to simplify my gear for blue water hunting, and no matter how I opposed the idea I could not get away from trying a bluewater reel. I personally think its nuts to shoot big fish with your gun attached to them, but I have read to many success stories of this method to discount the value of trying it out. Problem being where I am with limited spearos doing what I do is I usually have to try things MYSELF, which is expensive and sometimes even risky.
But anyway I bought this reel because of its line capacity mostly/mainly and in pictures its robust appearance.
Reel Ermes Sub Blue Water Leonardo 93
Well its not THAT robust but decent enough if your not a caveman like me with your gear! It is pretty though 
and after searching high and low for a sheathed/jacketed line over 300lb test strength I found this awesome but expensive Dyneema cored line, it is 2.1mm thick and it has a 250kg tensile strength or 551lb test strength with an exterior polyester jacket . I have seen wahoo chaff my cable slip tips so I wanted the most abrasive resistant stuff I could find.
Dyneema reel line for spearfishing / spearguns
The reel is supposed to hold: Capacity of the model Leonardo 93: 150 m Line ∅1.5mm ... well it is no where near that at 2.1 mm I can tell ya! I got over 250 ft on which is ok for me(i hope), but it doesn't add up with advertised capacity.
EDIT: I measured the line today, and the reel has on 312 feet of 2.1mm!!! Man that's a lot of line!
Anyway I mounted the reel by simply placing the reel where I wanted on my gun(as far back as possible) and using a sharp point from my leatherman I marked the holes, then using the same point I made pilot holes for my stainless steel marine self taping flat headed screws, not countersunk.
I measured my screws and then the depth of my track to make sure they would not go to deep and damage my spears epoxy track, determined the back screw needed a couple of washers and the front did not(two different sized screws, the back one being the larger/thicker)...A tip, the reel has a guide mechanism to spool the line for you onto the reel, the said mechanism has very little clearance off of the face of the mounting plate, if your screw head is big or you add a washer, it wont clear and will jam. Got out the 5200, forced as much as I could get into the pilot holes and then coated the screws... Screwed the reel on, and Bobs your uncle 
I ran my reel line through my line guide at front of the gun, then attached a snap swivel and pulled the line to my breakaway set up on my spear and simply snapped it on. Now if i want breakaway I unsnap the swivel and reel it tight against my line guide and I am back to a breakaway.
Front mount
Rear mount
The reel performed amazing while fighting a badly shot 20+ lb Dolphin, I had to put no pressure on the belly shot fish and allow it free run... the reel never tangled and was as smooth as silk both out and in, the drag system is a marvel.