Congrats on the purchase! Driving a SIIA like you intend to will make you a better driver in so many ways. It makes you patient, yours ears become attuned to the slightest change in noise, you learn to stop far enough back from traffic lights so you can see them, shifting gears becomes much more deliberate, you abhor tailgating, and you learn how much changes in temperature, air pressure, and humidity affect engine power. Mud tires really do have more rolling resistance than all-terrains, and concrete and asphalt also add different amounts of drag. You will find roads that you thought were level really have a slight incline. I think anyone who gets more than 6 points on their driver's license should only be allowed to drive a Series truck. Mine turned me from a speed demon to a stop-and-smell-the-roses driver. The effect on other folks is wonderful, lots of waves, lots of conversations at the filling station, and people actually let you merge.
We have the six-cylinder and a lot more weight, so after our second rear axle breakage, we put a Salisbury in ours (thanks Keith at the company formerly known as RoverTracks for contributing lots of advice and parts). When I had the transmission tunnel out I put sound insulation on the bottom side of it - it made a huge difference in the noise. If I ever take the seat box out I will do the same to the bottom of it. Make sure all the holes in the firewall and floor and seatbox are plugged up - it is amazing how much noise and heat can come through even a 1/4" hole. If I had a four cylinder like you I would seriously consider this for further insulation:
http://www.exmoortrim.co.uk/catalog...8-series-moulded-matting-system.html?sef=hcfp
Pertronix electronic ignition is a wonderful product.