I own a gts-t type M myself, so after a bit of research this is what I've found out about it:
"Not seen in too many parts of the world, the Skyline HCR32 GTS-t was a Japan only model, in Type M spec it has a 2L turbo 6 cylinder, producing 220hp as standard. With a few modifications the stock turbo is capable of producing up to 260hp, in Japan the RB20DET has been worked to 450hp by taking the displacement out to 2.4L, bigger turbos and other modifications.
Other Type M features include 4 pot front calipers in the front and 2 pot calipers in the rear, with a curious additional drum brake arrangement for the park brake, Hicas 4 wheel steering system that helps stabilise the rear coming out of the coner, Viscous LSD and a rear wiper. The Type M represents the top of the line of the GTS range. "