A 45 can be a pickup truck style, separate cab and bed or a really long wheel based 40 called a Troop carrier or Troopy with either removable hard top, soft top, no top or fixed=LV station wagon and comes in both 2 & 4 door versions.
LWB 40's are 43's. 44's are 4 door 40's... Confused even more ? :grin
And yes, you can tell them all apart once you get used to it.
I suggest flipping thru Aqualu and/or ICON/TLC's sites and look at the bare bodies, cabs and bed styles and you'll quickly have an ah ha! moment.
The different years are easier to tell apart. Pre 70 had round turn signals and tail lights, a 2 piece hood with a chrome ornament bar on it. Around 72 the tail lights went rectangular, around 78 the rear doors went from 3 piece to 2 barn door style, bezel went squared corners.
Engines F, 2F, gas, diesel, turbo and a plethora of Chevy and Ford conversions. 3 on the tree to 4 on the floor...
The 55 series Pigs and on up never interested me. I started this for the 40/45's and the old ad's. Yeah I should have labeled things better.
I bought my ARMY GREEN FJC because I had a '74 FJ40 in green.