Some assorted mounted points (stones) are useful, I just buy the cheapy Chinese crap ones. You can dress them to different shapes with a dressing stick for finishing in awkward places. The 25mm spherical one is handy for down in the ports on a 1275 head.
These stones don't last long, a carbide burr is best for main metal removal in the ports.

I use a piece of 8mm steel rod 120mm long with a slot in the end, for finishing in the ports. I wrap a strip of abrasive cloth in it. MUST run the die grinder slower, no more than 7000 rpm or so for this.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.