I use a course thread tap, and I used a slide hammer and clamped to the tap.  A few 'hammers' and out it came.

Just prior to the hammering , , I heated the surrounding area with a small propane hand torch.  NOT the plug/tap, itself, but the surrounding area.

The spent .45 ACP 'aluminum' cases just tap right in and 'looks' really good.

When using the aluminum solid plugs, I put in the freezer for a few hours or overnight, prior to tapping them in.  The COLD reduces the overall size a titch, and makes it easier to tap all the way in, (my opinion), <G>.

**If folks do this, then PLEASE, do NOT start the bike and run it, just after putting in the COLD aluminum plugs ! ! ! !    Let the bike sit for a few hours prior to running the engine. It IS possible for the aluminum plug/s to shoot-out of the hole, when the heads heat up faster than the plugs, LOL ! !  

**(This is one of those; Don't ask me how I know this !), <G>.

Joel 'Odo'