Decided to doom scroll through 'Mud this morning. I have worked in the off road aftermarket for years for both manufacturers and builders, I'm currently the GM for a fancy mostly Jeep shop in the Denver area...
You can get 90% of the benefits of going to coils by doing a small lift with nice aftermarket springs and shocks. My BJ74 on OME leaves and shocks drove great and was very comfy. I advocate for a small lift for most rigs because it allows you some space between the axle and bump stops, allowing the suspension to work. My advice to 95% percent of people coming to me looking to update a vintage rig is that if it came with leaf springs, best off spending a little bit of money on a nice leaf set up, investing in good springs and shocks, leaving you with money to do other updates. If you wanted to get fancy you can push your rear spring mounts back for a longer, flatter spring. Shackle reversals do help ride quality although they tend to cause nose dive.
The only exception to this is if you want to build some super high performance off road rig. If that were the case skip over springs and just go to a coil over/4 link or radius arm set up using easier to source quality aftermarket parts (I'm not super into radius arms for something with a lot of suspension travel that spends a lot of time on the street because of caster change during suspension cycling, but that's another debate for another time). Coil overs are race car parts and require race car type set up and maintenance, but once they are dialed you get a level of versatility that you can't get out of more basic set ups. If that's your thing it would be easier to source parts and create something better than the factory every came up with, performance wise, and you can choose your own adventure in regards to parts (I straight axle'd an explorer years ago using an XJ long arm 4 link set up for instance). Even the best, most well executed set ups like this are usually at the sacrifice of reliability. Toyota spent millions of dollars engineering Land Cruisers to be bulletproof, often at the expense of fun, excitement, and performance, a trend that continues to this day. Stock = reliable. Every step away from how it came from the factory means more custom stuff to do, and the potential for having to reengineer some aspect of the chassis to do something it wasn't mean to do. All this being said if I were to build an old wheeler, I'd still probably keep it leaf spring.
My $.02 but I have some experience in this arena, so figured I'd chime in.
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