Larsen makes a kit for this purpose https://www.universal-radio.com/catalog/hamantm/3083.html

You may need one of these https://www.amazon.com/Tram-1296-Nmo-Uhf-Adapter/dp/B00UMAVIZO if that CR8900 has a PL259 style connector. ninja edit March 24, no adapter needed, see more comments below. Thanks /u/DrMcMeow for setting the record straight.

You may need one of these https://www.amazon.com/Tram-1296-Nmo-Uhf-Adapter/dp/B00UMAVIZO if that CR8900 has a PL259 style connector.

why? the gp kit is just a so-239 barrel.