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Raceprops,
I don't know how you are missing the threads on the trucks, vans, and suvs on here getting good MPG, that is the reason I am a member of this site as opposed to others. There are several members on this forum getting pretty decent MPG out of vans, trucks, and SUVs, you should look to those threads for ideas. I seriously considered for a while modifying the 350 in my 1991 Chevy K2500LD for higher torque at lower rpm for MPG but ultimately decided to pursue other avenues mainly because it was a regular cab and I needed more seating.
You are correct that a high torque at low RPM engine combined with tall gearing is a potentially good combination for MPG in a larger vehicle. I don’t think there are a lot of people on here that are going to have experience with your specific setup modified in the specific way that you are suggesting, which is part of why you keep getting suggestions for other engines. I will refrain from suggesting other engines in this thread as you do not seem open to the idea.
My suggestion is that if you are set on using this engine modified in this manner, look to the other forums that have modified engines similar to this way (but for HP) and try to find a dyno sheet where you can get feedback on a torque curve. That should influence your gearing decisions on RPMs to run based on your torque requirements at a given speed. Sometimes they even have BSFC information on dyno runs. I am running a few engines in manners contrary to popular opinion with great success, but it requires legwork to connect the dots and sifting through lots of non-relevant information.
You also seem set on your transmission decision, but my personal experience is that stick shifts get better MPG than automatics with similar gearing. I saw a 4-5 MPG gain swapping a 4l60e (11-13 MPG) to a NV4500 (15-18 MPG) in my aforementioned 1991 K2500LD, note that the overdrive ratios of the two transmissions are very similar and no other changes were made to the vehicle. Treat that as a data point and draw your own conclusions, many people prefer an automatic for other reasons.
My experiences with tires has been different than you suggest, I strongly prefer stock or narrower tires on my vehicles versus wider. I may be leaving something on the table in dry weather, but in adverse conditions I have had much better luck handling and braking. To me tire width should be a function of vehicle weight and PSI to maintain a similar contact area force. However I have found tire tread pattern has just as much to do with it as size, I prefer tires with large amounts of sipes. Back when I had a sporty car I had "hard" tires outhandle "soft" tires in all conditions because the tread pattern was better despite the rubber compound.
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