How to upgrade felt MP beach cruiser (steel) with cool bottom bracket using adapter

[Showmepictures]

I wanted to get new pedals and try out my fyxation straps. Of course, I found 9/16" pedals I preferred that don't work with the current one piece crank and now I'm tempted to go down the rabbit hole upgrading my bb and crankset.

What BB's could I use with this:
black ops adapter ( https://www.amazon.com/Black-Ops-Conversion-American-Silver/dp/B00JWZXVRS/ )
I would like to install something modern like hollowtech II, dub29, gxp sram?
Or is there another adapter type for the BB styles mentioned above?
I don't want the cartridge JIS taper style if possible.

Been going down the rabbit hole, reading many posts, finding similar stories, but wondering if someone could point me in the right direction. Something similar to Chad T's scrambler and collegeiate, but I couldn't find the details.
Gigmata said commented they were trying to installing FSA BB in felt cruiser, but not sure how it ended up and couldn't see the pictures.

I have to measure the shell, but believe it is 68mm wide, id 2.02" or 51.3mm and chain line of 50mm.
I know bmx crank set and 19mm american bb could work, but I really don't like the look and price of bmx cranks.
I do not want to use pedal adapters to convert from 9/16" to 1/2" and extend the pedals out.

 

[Captain Awesome]

You can use that adapter and a threaded BB to get a hollow tech setup mounted. Chainline tuning will be the struggle. Definitely have to bring the drive side of the crank inboard tight and possibly a dished rear cog

https://www.bikeforums.net/bicycle-mechanics/1229642-hollowtech-2-mtb-bb-68mm-road-bb-bike.html

This mainly focuses on bikes with derailleurs but good info

 

[Captain Awesome]

FSA used to make a very nice 2 pc hollow core bmx crank set that was for American BB but that was years ago. Basically MTB looks in a BMX frame with no special hardware