#1
Ok I picked up a 95' or 96' Ibanez Silver Cadet for £45 off eBay. Pretty nice for the price but the hardware is crap! So I'm gonna go with a "blackout" on it. Already found the trem I want but the tuners are a problem. They're the cheap-o hexagonal Gotoh copies. I need some advice on which tuners I might use as replacements. Black please and note that I'm in the UK. I wouldn't have a problem going with single screw mounts either. Thanks in advance!

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#2
I would just drill the headstock for a set of locking Schallers. It's unlikely you'll find a quality set of machine heads that will drop into those holes without any drilling.

I'd pull one of them off and measure the post hole (the big one). Drilling the small holes for the set screws isn't a big deal, but you're better off not messing with the big ones if you can help it. Stewmac has the dimensions of all their machine heads on their website, you'll be able to find a set that at least fits the post holes properly.
#3
It really all depends on how much you want to spend. For tuning stability I would consider getting a new nut also. If the hardware is crap I am guessing the nut is too.
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