import template of 7750 without ncm connection to internet

There is a place in-product to view community driven templates for NCM. In your SolarWinds web console navigate to:

Settings > All Settings > Manage Device Templates > Shared Templates on Thwack (tab).

You can import it directly into your deployment. The template should attempt to 'auto-assign' based on the System OID from the device.

You can also see that per node by clicking into any node and looking at the 'Node Details' widget

If those numbers are off/different, you can update the NCM Device Template accordingly so the auto-assign will function.