Tony,
Your 408 will be right for Group 2 as you said, the 310 Cadet is perfect for Rook and Rabbit Rifle.
If your 450-400 does over 2900 ft lb of energy you can use it for Group 1.
We won't be sticklers for the limits though, shoot what you like.
As Neale said, he has a spare Group 1 rifle.
I've got a Sako L-61R in 35 whelen you are welcome to use as well if you like.
Don't worry, we'll find enough guns for you to use!

Regards,
David.