I am just curious why you feel the need to replace the stock tonearm, insofar as the ones you are considering are not obviously superior to the original. Also, you say you must have an armboard available for purchase. Lots of luck with finding a ready-made product to suit.
If you choose a tonearm with a similar pivot to spindle distance to the OEM tonearm, and if the diameter of the vertical shaft that must mate with the armboard is in the same ballpark and can fit through the existing hole, then you may not need an armboard. But these requirements will dramatically limit your choices, if you feel you must go ahead with the replacement process. Instead, you can buy a slab of brass or aluminum (two materials I recommend for the job), have it cut to size by a machinist (just remove the OEM armboard and measure it, to determine the needed length and width and where screw holes need to go, etc.), and then have it drilled exactly where you want to locate the pivot with a hole that is exactly the proper size (by the same machinist) to suit your new tonearm. That way you can have nearly whatever you want in the way of a new tonearm, so long as the P2S fits the available distance. "On-line Metals" is one company that sells what you need; they'll even cut it to your required size. Colby Lamb, in Oregon, is an audiophile/machinist who would probably be happy to do the work for you. The onus is on you to make the needed measurements. I’ve done this sort of thing at least 3-4 times, painlessly.
With all due respect to Sleepwalker, he does not seem to get the fact that the new line of SL1200 turntables (the G, GR, and GAE) are miles ahead of the original SL1200 series in terms of isolation and footing. This I think is why he recommends the footers. On the other hand, one might say that any turntable can benefit from thoughtful attention to isolation. But in my opinion, your GR "needs" it much less than Sleepwalker's much older SL1200 (or SL1700, which is what I think he uses). Sorry, sw.
If you choose a tonearm with a similar pivot to spindle distance to the OEM tonearm, and if the diameter of the vertical shaft that must mate with the armboard is in the same ballpark and can fit through the existing hole, then you may not need an armboard. But these requirements will dramatically limit your choices, if you feel you must go ahead with the replacement process. Instead, you can buy a slab of brass or aluminum (two materials I recommend for the job), have it cut to size by a machinist (just remove the OEM armboard and measure it, to determine the needed length and width and where screw holes need to go, etc.), and then have it drilled exactly where you want to locate the pivot with a hole that is exactly the proper size (by the same machinist) to suit your new tonearm. That way you can have nearly whatever you want in the way of a new tonearm, so long as the P2S fits the available distance. "On-line Metals" is one company that sells what you need; they'll even cut it to your required size. Colby Lamb, in Oregon, is an audiophile/machinist who would probably be happy to do the work for you. The onus is on you to make the needed measurements. I’ve done this sort of thing at least 3-4 times, painlessly.
With all due respect to Sleepwalker, he does not seem to get the fact that the new line of SL1200 turntables (the G, GR, and GAE) are miles ahead of the original SL1200 series in terms of isolation and footing. This I think is why he recommends the footers. On the other hand, one might say that any turntable can benefit from thoughtful attention to isolation. But in my opinion, your GR "needs" it much less than Sleepwalker's much older SL1200 (or SL1700, which is what I think he uses). Sorry, sw.