What makes you think a turboGV has never been done?
Depending on which part of the world you're in, you can walk in to the Suzuki dealership and buy one - the GV is sold with a turbo diesel, and it's quite popular over in the UK & Europe.
Since what you want to do is put a turbo on your H25, search the forum for a user called TurbineTech and drop him a pm - he's a french canadian guy runs a turbo charging business, I don't know if he's worked with the H25, but memory says he built a TurboTracker a while back
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