I probably bought wrong 8 3/4

Joe, great help. If I were to take this 8 3/4 case and have it professionally converted to the suretrak 3rd member and axles, green bearings etc. can I expect those parts to be available unlike the difficulty I encountered just finding my 66-72 full axle (which I now feel very lucky about). Where would I start? I just want highway gears, but do I go to a tranny shop or speed shop. Any notion of what this extra would set me back for?