Tonearm for Technics SP-15

I have a Technics SP-15 turntable with a Grace 707 arm and a Grace F9E cartridge with a Soundsmith new stylus.  This combination sounds great but is limiting.  The 707  tonearm has a fixed headshell and it does not allow me to easily swap other MM  high compliance catridges or match compliance requirments MC cartridges.  Suggestions welcome from those more expert than I.  

Post removed 


The 250 comes with 3 different arm

To be precise, I would like to underline that Epa 500 is only the common base for all arms compatible with this.
Then there are these barrel interchangeable for base Epa 500
Epa 250 has an S-shaped barrel and a shell with an interchangeable ​EIA attachment.

Barrel with fixed shell
Epa 501 H
Epa 501 M
Epa 501 L
Epa 501 E
Epa 501 G

each arm has a limited range of compatibility with the cartridges to be used depending on compliance

I own a B500 with the EPA250 arm wand and a 501H.  Unfortunately the base is so "fat" that it really will not fit any of my turntables except my TT101. But I have an FR64S mounted on the TT101 specifically for low compliance LOMCs.  I'd have to machine a new tonearm board for the B500.  (I use a solid aluminum armboard that is further braced from below by fastening to an even larger piece of alu.) But the B500 is an esthetically beautiful piece of precision engineering the likes of which would cost a fortune in today's money.