Conversion? I recommend "not". Future GAS considerations? Sure
!
I considered my Bassman 500, actually intended
before the R500c so pleasantly distracted me (Gee, was it really
8 years ago now?

) to be an adventure in vintage tube head
looks (without the weight) and my first SpeakOn requiring amp, or so I thought. To my giddy surprise it arrived with the
7ender amp cover, the channel-changing footswitch and a short SpeakOn-to-SpeakOn cable that was perfect for my cart-before-horse year older Bassman Neo 115 cab
!!! 


Then one fateful day, while gazing lovingly upon my SpeakOn clad beauty, I actually read the back panel.
"What's this 1/4" JACK COMBO bidness
?!?", says I. An' Oh, lawdy, Miss Claudie, did I whoop when I tried a 1/4" speaker cable and it worked just fine! Woo hoo!
Now. IIRC our esteemed
ElderEquine says some countries require SpeakOns for as little as 400W, or so. Therefore, perhaps the SpeakOns on the Bassman 500, which can only see a maximum of 350W when used properly, are more for professional, if not vintage, good looks than actual safety, I dunno. 'Cause if truly for safety and sales 'round the world, wouldn't they also be on the Rumble 500s, as well?
.