Paul, check out
this link for a brief description of the difference between mechanical and electric gauges...
The difference between the 4347 and 4348 oil temp gauges is the range: 4347 is 100°F to 250°F and the 4348 is 140°F to 300°F. I believe the 4347 is the most useful for our purposes. 4356 is the "full sweep" version that has a range of 100°F to 340°F.
The matching trans temp gauge is the 4357, as you found.
As for the "full sweep" description, most electrical gauges are a 90° sweep (indicator range), while most mechanical gauges are 270°..."full-sweep" (270°) electrical gauges are relatively new and are generally about 3X the cost of a 90° gauge...