If you want to install to the oil pressure switch boss, that is a better choice than the oil test port. Is there even room to have a sensor sticking out under the fairing at the oil pressure test port? There was not on the 14 so I doubt there is on the busa. You would need to use a high pressure hose to place the sensor in a remote location so it won't hit the fairing.
Buy an adapter with ports for your oil switch and the oil pressure sensor.
You don't want to screw the oil pressure switch boss up or you get a new oil pan or have threads retapped. If you bugger the threads on the test port....dang---pretty hard top replace that!
I recently installed an oil pressure gauge and oil temp gauge to my 14 and I had exactly the same conundrum you are having. I just could not figure out for sure what thread the oil pressure switch was. Turned out it was 1/8" NPT however, the threads in the oil pressure switch boss were cut smaller than the typical 1/8" NPT male fitting. Remember, these are tapered threads so there is no definite OD established. They can be tapered smaller or larger. Compare the oil pressure switch thread diameter to the thread diameter of your sensor. If they look very close in diameter, then I would say you probably have different threads on each. Interlock the threads of the oil switch with the threads of the sensor. Do they mate up?
It should not matter very much if the threads are BPST or NPT. NPT are 27 threads/inch and BPST is 28. They are almost interchangeable and as long as you can get a turn and half past max hand tight on it, it should seal with a high quality, high temp, automotive grade teflon tape. Also not an issue if these are JIS tapered threads because that is identical to BPST.
I believe the manufacturers of motorcycles do not want you to put anything but an oil pressure switch in the oil pressure switch boss. I had this "extra small diameter threads" problem on my little Yammi DT-100 back in the 80s and then again on my ZX-14. You might have to mod as I did.
If it's simply a mater of Suz making the thread diameter extra small,
get an adjustable die. Cut the male threads on you adapter smaller in steps. I had to go all the way to the smallest adjustment on the die.
I did a huge amount of research on this. If you think your problem is the same as my problem was, you might want to spend the time reading my tutorials on this. At least it will give you all the info. It's for my ZX-14 but all might apply to the busa.
Happy reading. There are multiple links to other info on both of these. Feel free to ask as many questions as you need. I had a heck of a time figuring this out and would be glad to help if I can. It is not such a big deal once you did it but you are extremely wise to proceed with caution as a total beginner.
OIL GAUGES ADAPTER MOD
http://zx14ninjaforum.com/messages.cfm?threadid=BB62166E-1B78-59F6-02EF1E37066C179C
INSTALLING OIL GAUGES
http://zx14ninjaforum.com/messages.cfm?threadid=88999CBD-1B78-59F6-022D4D67180D8E33&page=1&searchTerm=Oil Gauges Install#1
One last tip for now: don't bother installing an oil temp sensor to an external adapter as I did. The oil flow is almost nothing in the adapter. Work great for pressure but barely registers any temp change at all. For a temp sensor, you would need to drill and tap in the oil pan. A remote adapter with hose would be useless.
