Another option is to use the seat you already have and get better shocks.

I know you probably want to keep it low...these 11" shocks are a HUGE step up from the stock shocks. The 12" version would sit you an inch higher, but the quality is superior to the stock shocks on a Touring model. Very good road feel, and plenty of well dampened travel.

 

Let's be real NO seat that looks cool is comfortable and they will all make your sack numb after 25 miles I don't care what shocks you have. Only option you have is to install the gigantic monster thick seat and add a windshield and saddle bags then wrap some white tape around the bridge of your safety glasses and post in the "Show pictures of your bagger" thread.

 

lol sad but true. luckily I have a nut saving bagger...

 

my 48 is a 2014. my buddy is taking his shocks off his 2016 and giving them to me, i'll see how that goes.
I already sold the mother road customs seat. my last trip on it was over 250 miles, almost brought me to tears lol

 

Disagree about the seat and comfort. My mustang, although not looking comfortable is. Frequently ride 70+ miles with no issues. I am an old guy too. Shocks helped but I think the stock tires are a lot of the issue, I feel all the small bumps and ridges in the asphalt. Reducing tire pressure to 36 front and rear has helped.
I have other bikes the 48 was for looks and image "old school" but I do want it to be at least comfortable to ride shorter rides.

 

Agree with the OP that curved steel plate type solo seat should fixed to the frame with rear spring shock mounted bike.
With a spring suspension solo seat combined with rear springs it creates what is known as a two degree of freedom spring mass mechanical system.
The two springs can be in phase or out of phase. When the two springs are in phase , both springs move In equal directions, either up or down.
When the two springs are out of phase, the rear wheel spring can be compressing , while the seat spring is extending and vice versa.
That means the bike frame can be moving downward while rider is moving upward, not good. To be in control both the rider and bike frame need to move in the same direction.
Believe the spring mounted solo seat is perfect on a rigid frame bike without spring loaded shocks.

 

I don't have a mustang, so i'm not sure what your disagreeing with lol
and 70 miles I can do, the discomfort on my frame on seat starts around 125+ which I do often.

 

The frame mounting plate used by newto48 is a Mustang part number 76629, made of marine grade moulded fiberglass , this the cleanest method and covers all the internal components and wiring,
for a solid mounted solo pan type seat.