[Jeff Lee]

The performance gain will be in using the lightest weight parts you can put in the rear; from slick to slick. That includes the wheels and possibly using a lighter slick by going smaller in both width and diameter and adjusting the gear ratio as needed. And since there won't be much power, I would suggest a light-weight aluminum spool. Since this would be the lightest, that answer's the question on the posi unit. And I would find the lightest wheels available and no wider than 8". Personally I would be looking at 7" wheels with 8" slicks and running Cal-Track bars, springs & shocks. And you can also get away with a small diameter / thin wall / lite driveshaft.