You might concider removing some of the magnesium, but not all of it. I just got done letting the Workshop Of Doom *tm* alter one of those 3"x1"x3/8" stock ones.
Oddly enough the cheap coghlan's has a larger flint than the mil spec one I have.
Anyway I wanted a small keychain flint, and around here the pickings are very slim for choices. So I bought one of those large magnesium ones and used a hacksaw to cut it in half both the width and height. What I ended up with was a 1.5" long by 1/2" by 3/8" square magnesium block with a 3/16" flint. This could be rounded off with a file if you prefer as well I just left it square and rounded the edges.
Now I know magnesium has a lot of drawbacks but there are a few reasons why I left it on the flint without removing all of it.
First the magnesium supports the rod, flint is brittle, and with only 1.5" long if it broke it would be hard to use the broken parts. On such a short peice it would probably be hard to break, but better safe than sorry
Also it provides something to drill through and attach to a keychain. Though drilling through flint could be fun
And I look at it like this, sometimes for whatever reason some things work better under certain conditions and I'm convinced magnesium isn't the ideal tinder. It takes more time to get going than just using dry tinder the only real drawback to having it is the extra space. It doesn't hurt anything and sometimes it works very nicely to get tinder going (or maybe I'm just pyrotechnically challenged). It certainly can't be your only tinder, and the scrapings blow around in the wind. But maybe it gets that one fire started that the big ol' strike force just dosen't wanna.
And the best reason is the hacksaw makes really sweet sparks going through the flint
I also made sure to keep the left overs and saw leavings for other workshop of doom productions.
For a striker I took a 1.5" peice of hack saw blade, left the saw part (it really throws the sparks if you need it to). Then sharpened the spine and end as to have two good striking surfaces that unless you really beat down on the flint won't gouge it.
This I then electrical taped to the flint and put it with 3 tinders in my project I handle. The other half I will make a striker for and electical tape or duct tape it to the flint and put it on my keychain or maybe heat shrink together but that could be harder to get at in the time of need.
So for $6 I got two keychain sized 3/16" flints with magneisum, and a good hunk of magnesium left over and half a film canister of saw leavings.
I also plan on trying one a bit longer maybe 2.5" X .5" X 3/8" on the keychain, but trying even this 1.5" model with the sharpened saw blade you can really throw the sparks, even more so with the teeth side if you have to.