What outdrive do I have ? 72 bayflight

[Robzilla31]

Hi.
First post
I found a mint 72 Glastron bayflight 164
Im looking for a prop but I dont know what drive I have ( no paperwork )
140hp mercruiser .
Right now Im doing 33mph at 45-4600 rpm with a 25" prop
Whats the most rpm I can run with this motor ?
Thanks ...