What’s the bolt pattern like?
Did you check won’t a Busso flywheel fit?
Busso DMF is the same weight the 2.5 is just over 7 and the GTA just over 6kg if I remember correctly.
Long ago I read a study that showed that 1kg of rotating mass removed equals 10kg total mass removed from the body when it comes to acceleration.
The study was performed on a old GTV6 if I remember correctly.