T5MalibuWagon,
The improvement in mpg doesn't have to cover the cost of the changes I'm making. I'm planning to switch the thermostat, add a windage tray, change the carb and possibly upgrade the ignition while I'm changing the cam. Fuel economy is a quest of mine, so if the changes I'm making result in an improvement, I'll be happy with it. As far as whether the improvement in mpg DOES pay for the changes, that will depend on how large the improvement in mileage is and what the price of gas becomes. Between the problems in the Middle East and the increased demand for oil from China and India, I'm planning on the price of gas exceeding $5 a gallon and wouldn't be surprised if it exceeds $10 a gallon in today's money.
Currently I'm getting 20-23 on the highway, about 16-18 in mixed driving and would be doing well to get 15 around town. Part of my problem is that my 3470lb wagon is a bit heavy for a 4.3L V6, and having a larger than stock cam isn't helping matters. Another problem is that the 3 speed manual trans with 2.73 rear gearing means that I really don't have a good gear for driving in the 30-40mpg range around town. I have the choice of puttering around in 3rd and dealing with the loss of vacuum due to high loads at low revs or keep her in 2nd and have the revs higher than I like. My ultimate solution would be to install a 5 speed, but I hope that switching to a milder cam will improve my low end torque situation, making 3rd gear more useable. I also hope that it improves vacuum and mpg at all speeds.
Given your comment on LSA, I take it you think the Crower would be a better choice?