So I'm looking at a t28 to supplement my need for a turbo, but my question is will it fit on an HKS manifold? Most sites show that it fits a t25, but I'm not sure if the flanges are the same.

 

im almost sure its the same flange,the difference between a t25 and t28 is the t28 has a bigger intake fan and housing.

 

As stated above. The t28 uses a t25 flange but the compressor is bigger. You will have some clearance problems with the larger t28 because the hks outlet is on top. I had to notch my hood bracing to fit a t25.