Long cutter, radiused end so it won't dig in and produce a straight deep cut at the end.
Also small diameter so the inside corners of the LIM runner outlets match the inside corner radius of the cylinder head.
For L67 and L36 LIMs, this isn't going to do much for you. POSSIBLY for L27 LIM runners.
On this page:
The best I would select (based on my preferences from past experience with superchargers and LIM'*):
(great for inside corners and 'shaving' for finish work)
(very handy for coarse material removal and working the inside corners of L36 runners)
(good for opening up a chamfer blend on the INSIDE of L67 runners from the OUTSIDE).
Don't forget, polishing is cool, but won't really gain you much performance if you get a nice finish with a carbide. Polishing well MAY help reduce the buildup of EGR and PCV crap over time.
Sanding drums are a PITA to change, and aren't really needed if you work it carefully with these carbide bits.
Do NOT over-port. You want the finished LIM outlet to be equal to or slightly LESS than the width and height of the head ports (approximately 1.9 by .9 inches). SLIGHTLY break or round sharp exits and entrances. If you do that on the cylinder head while installed on the engine, STUFF THAT port with paper towels or small bits of rags, seal off the lifter valley, and use magnets and VERY careful techniques to pull the stuffing and clean up.
As mentioned by a couple of us in this topic, oil will lengthen the life of carbide cutters almost indefinitely when used for aluminum.