FX guys. Wildcat MK2 questions?

Please help me understand the mk2 vs mk3. When I look up barrel kits all I see are mk3 complete kits. Does this mean that on the mk2 only the liners are swappable? There is no easy way to swap a whole kit for a caliber change on the mk2? Any clarification on the barrel differences would be great. I know the mk2 does not have an externally adj reg like the mk3 but still confused about barrel diff. Thanks.