...a 5.17:1 gear. Does that sound right? If it could be, then I would be happy as that is in the range of OK for the diesel conversion I would like to do....
Even with an OD and 40" tires 5.17 sounds way to slow for a diesel conversion.
For example I've got a 0.80 OD, 38" tires, and 3.54 gears (may later want 3.73), for sure not 5.17.
But it all depends on the engine you choose and how fast you want to go (or can go) with how much of a load.
Try a gear calculator like this to plan what ratios and combinations may work well.
http://www.onlineconversion.com/bigger_tires.htmHave any more details on what conversion you have planned?
Grigg