Do you know if the Tremec 600 has the same bellhousing bolt pattern as the Saginaw? Do you have bucket seats? The pics which I have seen show the shifter positioned quite far to the rear. Maybe some of them aren't like that.
Yes, the Tremec transmissions have several options for the shifter location. I do believe the kits available to move the shifter to the “mid-shift position” are pretty pricey. Just depends what you want and the application.