So are you using carbon arrows then?The only 125 gr brass adapters I know of are for gluing in a carbon shaft and take the place of adapter and insert.If that is what you are referring too,yes,they would be perfect.I have some here and tried one in a Razorhead.They don't block the slot.
A 75 gr steel adapter,at least the ones I have,also work.You would need an insert of your choice with those.You could use inserts of aluminum of app. 14 grs or 50 or 100 gr brass.
Actually,that is more options for use with the Razorheads than I thought there would be.