The most obvious external differences between the Grumman F8F -2 Bearcat in the lead picture above and the F8F-1 were the 12" taller vertical fin and rudder and the 20mm cannon armament (the latter was also a feature of the F8F-1B, the B suffix indicating a change in armament) indicated by the longer barrels and the bumps on the upper surface of the wing.
A not so obvious difference was the windscreen. See http://tailspintopics.blogspot.com/2016/07/grumman-f8f-bearcat-windscreen.html
There was also a difference in the engine installation. Reportedly (see Davis Gandees comment below and HERE:) only the first 23 "pre-production" F8F-1s had 5 exhaust stacks.
According to Gandees (and a subsequent comment by anonymous), the remaining F8F-1s had three exhaust stacks. The following sketch showing a fairing added to the trough to cover two lower stacks is is therefore incorrect.
The -1 shown here has the production exhaust trough with the lower side raised above the wing to smooth the flow over the wing and horizontal stabilizer.
Air that had passed through the oil coolers was dumped through two "shutter" controlled doors between the inner main landing gear doors. These are the doors on the F8F-1:
These doors were a slightly different configuration on the F8F-2. They were longer, extending farther forward, and had a scalloped cutout on the inboard side.
A fixed oil cooler vent was also added across the bottom of the aft end of the -2 cowl (Mark Hayward picture from the Prime Portal F8F Walkaround):
Mike West of Lone Star Models sells resin 1/48 F8F-1 and -2 cowls as well as other F8F improvements. Chris Bucholtz of Obscurco also offers a replacement F8F-2 cowl for the 1/48 Hobbycraft kit.
For much more detail on the F8F Bearcat and operational usage, see Steve Ginter's excellent monograph written with Grumman's Corky Meyer. It's also available from Sprue Brothers.