Both say that internal mods are needed but what does that consist of?

Since the turbo needs to be modified, could i do it my self or is it better for me to send it off and spend the 85 for them to do it?

What is the difference in the performance of the GDS 8 blade 60mm wheel and the 6 blade 60mm wheel?

 

Good luck with that. I called HTT and they basically blew me off.
I just need to get my compressor cover machined. I already have the 35/40 center section.

 

Your stock HX35 compressor wheel has a 78mm major diameter. The HX40 upgrade 60mm compressors have an 84ish mm major diameter so the center section of the turbo need to be milled a little so the larger diameter wheel can fit. No need to machine the compressor cover since the upgrade comes with a new larger cover that is matched to the 60mm wheel.

The difference between 8 blade and 6 blade 60mm wheels is slight difference in airflow and larger difference in sound. The 6 blade wheels SCREAM but they do flow a bit more air.

 

I have the 6 blade 60mm x 86mm compressor.
I've been contacted by someone at HTT and hopefully can get this done.

 

Could it be machined by my local machine shop pretty easily?