TT Arm compatibility.

I think that most of the 9” arms would fit. Accordingly to the mounting plate there will be no problem with fitting up.
http://www.canuckaudiomart.com/view_images.php?cat=Analog&catnick=analog&cfid=149145&image_id=1242386
http://www.soundfountain.com/amb/ttadjust.html#VTA
There might be a problem with high arm regarding the dust cover height.
So, get the best tonearm (and the cartridge) you can afford.

"How do I know what arm I have now?"
Simply, if the inscription/label on the arm is Ariston, then it is an original arm (see http://www.vinylengine.com/phpBB2/album_showpage.php?pic_id=2553). If the inscription is something else, use Google. If there is no inscription, take a photo and mail it at Audiogon Forums, Audio Asylum Chat etc.
The question is: why do you wish to replace the existent arm? Is it damaged or do you look for an upgrade?.
Not at last, choosing tonearm you must pay regard to the characteristics of the existent cartridge.