9/32 is the diameter of the shaft, most adaptors are 5/16 or 11/32 and they will work with Beman Classics. The shaft is going to be smaller than back of the head. Beman Classic’s use the HIT (Hidden Insert Technology) insert, inside the shaft, nothing exposed.
Beman MFX Classics are the same as any other arrow when it comes to broadheads...use a standard thread broadhead. If you use a broadhead that is a glue on type you'll need a broadhead adaptor of some sort i.e. aluminum or steel.
If you get a stiffer spine 400 and lower, for a bow that is lower poundage (around 50) you’re going to need more weight up front. From what I’ve read on here and heard most people with bows around 50 lbs and a standard draw of 28” need around 200 to 250 grains up front with a 400 spine arrow. This will require a large heavy head like Muzzy phantom 220, Razorcap with heavier ferrules or something that will get you to that weight. Like a 100 grain steel adaptor and a 125 grain head like a WW.
The other thing you can do is replace the aluminum HIT insert (if I remember correctly weighs 14 grains) with a 100 grain brass HIT insert and use any standard head on the market…this will allow you a larger choice of “mainstream” heads. If you like a particular glue on broadhead that is around 100 to 150 grains use the supplied aluminum HIT insert and a steel broadhead adaptor to get you to the correct weight up front.
I use a 30.5” Beman Classic 500 spine with my Savannah longbow and Kota Kill-um recurve. I shoot both drawn to 29.5”, my Kota is 46 lbs and my Savannah is approximately 53 lbs at that draw length. I can shot the same arrow from both but need a 125 grain head with my longbow and a 145/150 grain head with my recurve. This fall if I hunt deer with my Kota I’m going to shoot a threaded WW or a Razorcap with the ferrule that gets it to the 150 grain weight, more than likely it will be the Razorcap since I could use it with both my longbow and recurve, just change out the ferrule.
Looks like I rambled on for a while so I’ll wrap it up…hope this helps.
Josh