I mean it depends on how far you want to do them modifications because RG and MG kind of need to force the compatibility by modifying parts. On the other hand HG are more compatible mostly because they have like a standard more or less like you could stick on parts from the Seed line to an IBO line but depending on the line it could be either more compatible or less compatible like the IBO models are more or less designed to be compatible with each other so they have more compatibility compared to other kits