An HSSI Port with a CAB-HSI1 will give you one single port. I don't know any NM that will give you 8 HSSIs on each NM. I don't think there would be room for the connectors. If you want 24 HSSIs, I guess you will have to go to something bigger.
Having said that, is it really HSSI you want? How fast do you want these interfaces? There is an 8-port sync/async card that will go on your 3745, but each port is limited to 256Kbps if my memory serves me right. If you want 2 Mbps, there is a 4-port NM.