For sound in the front of my 240Z, I installed speakers in the kick panels... but this might be more difficult depending on year, in '72 the fusebox was in front of the shift lever (is it there, or in the passenger side kick panel, on yours?)
Now, there are many schools of thought on this one. I used 1/2" MDF, painted flat black to blend in to the surrounding area. (I'm sure there are folks reading this who cringe- but here's my reasoning. Nissan used *cardboard* to trim this area of the car. Not excusing their cheapness- but if I were to build curved fiberglass enclosures and finish them in tweed, I think it would stand out like the proverbial sore thumb. I'm not into attracting attention after I had my MTX 10" subs and boxes stolen.)
Current setup: Infinity 5.25" in rear corners, JBL 6.5" in kick panels, Pioneer cassette, Sony 10-disc, Rockford 8" sub behind passenger seat. Amps by ADS, and you know what? At 90 MPH, the 2.5" exhaust still gets the last word!
Rob