I think 2009 was the last year for the Long bed(7' box) Rangers, these were all Regular cab models
These have a different rear frame so its not possible so swap a 7' box onto a 6' box frame, unless you also swap rear frame section
Regular cab or extended cab Ranger both used the same 6' bed and are interchangeable
Either size box, 6' or 7' can be fitted with a bed extender, this gives you the folded down tail gate length added to bed length, tailgate is about 17" tall, so 6' bed would be close to 7.5' with tailgate down
There weren't alot of Long bed Rangers ordered every year, so finding canopies or tonneau covers can be tough, not a big market for 3rd parties to make them
Same for replacement beds if it gets damaged
So grain of salt
Yes, from about 1998 no 4x4 Ranger had a 4cyl option for the engine, all were V6 only