Do Beuchat offer a roller kit? If so, they might be able to offer guidance(e.g. confirm that trigger mech and spear are up to it). An inverted roller might overgun it.
If the kit is for standard 28mm barrels and if your speargun has such a barrel I would think there is a good chance that it might fit but check the specs .
Spearfishingstore.co.uk periodically have the keenly priced Apnea roller kit (about £40) on 20 or 30% discount. They offer 2 versions, the oval one which is specifically for the Amarok model (my speargun) and the other is for most of their other models except the small, cheap model, which likely have unrailed 25mm tube barrels. The latter might be fairly generic (check!) For 28mm tube barrels, although it occurs to me that several models that use it, such-like as the Whaler, have railed barrels and the barrels look different to, say, RA railed barrels, which may or may not be important. These are regular rollers though, not inverted.
Alternatively, why not buy an Apnea Whaler or Amorak roller gun when they are next on sale (e.g. 75, 85, 90, 95 or 100cm model)? Probably around £100-£120 when on sale - great value I think (I bought the Amarok roller gun). Or just fit twin 14mm bands to your existing speargun - fashionable, cheaper and simpler?