Mike:
I'm sure you realise the difficulty of altering the chambering on a pre-WWII Mannlicher due to the precise fit of Otto Schönauer's marvellous rotary magazine. The problems involved in altering the 6.5x54 to the 6.5x55 would be insurmountable I suspect, due to the greater cartridge OAL and the much larger case-head diameter of the Swedish cartridge.

If you want to do that, a rebarrelled M1905 might work (if you could find one!), otherwise you may have to stick with the post-1950 box-magazine variants.