After getting three speeding tickets followed by a suspended license on my Kawasaki LTD 1000, I bought a 1981 Wide Glide Shovelhead to slow me down. Ended up putting in a 96 inch S&S Stroker kit, Manley valves, solid lifters, S&S Super carb and Andrews B grind cam with open drag pipes. Harley made 1200 cc (74 cubic inch) Shovelhead engines then went to 1340 cc (80 cubic inch) in 1980, but all they did was to bore out the cylinders to a larger diameter. This reduced the cylinder sidewall thickness and became a weak spot near the base stud area that had clearance relief cuts outside the cylinder for the cylinder base nuts. The rear cylinder exploded on mine and that is the reason for the Stroker kit. Good thing that model had forward pegs and controls or I would have had shrapnel in my legs. The Wide Glide model had a kickstarter and electric starter with a 4-speed transmission. Lots of fun kick starting a stroker...
I rebuilt that engine three times during my stint in the Navy, then picked up a 1992 Fat Boy Evo Orange/Cream edition that was owned by a Harley mechanic. He installed lots of aftermarket goodies plus an Accel Fuel injection system and it was faster than the Wide Glide. I put on Samson Long Cannons with no baffles and was able to hit 105 in 4th gear and this was a 5-speed. But these bikes put out maybe 58-62 horsepower.... The Fatboy was stolen from the apartment complex and I had sold the Wide Glide to my girlfriend of 10 years, so no bike for a year until I picked up an early production 1999 Fat Boy identical to the Terminator 2 motorcycle for $9000. That was the last of the single cam design. The prior owner put on a Vance and Hines 2 into 1 Pro pipe, but otherwise I've left it stock and still ride it for short trips. All three of those bikes had solid mounted engines and the Softail runs twin horizontal shocks under the transmission. The stock shocks are not great and my Spousal Equivalent won't ride on the back anymore.
Pros for the Evo Harleys are single cam, single carb, two spark plugs, belt drive, heel toe shifter (for me anyway), dry sump oil system, simple design, tons of aftermarket replacement parts, easy to work on.
Cons are poor handling, old design frame, engine and transmission, suspension, brakes, primary chain, expensive, reliability (likely due to air cooling vs. water).
The issue with the 2003 Fat Boy is the Twin Cam design. I would stay away from a Twin Cam engine and find a nice Evolution engine Fat Boy. The model design from 1990-2017 did not change in appearance much, so they are all similar looking bikes.