I ended up doing this to my 48V Club Car yesterday, largely based on this writeup.
These are the batteries I used: https://www.amazon.com/dp/B099HSKY5X?psc=1&ref=ppx_yo2ov_dt_b_product_details
This is the charger I bought: https://www.amazon.com/dp/B0B1CXL6Z6?psc=1&ref=ppx_yo2ov_dt_b_product_details
Like OP, I simply cut the end off of that charger and spliced my old charger head end to it so that I could use the OEM charging port and didn't have to have access to the batteries to charge. Worked just fine, and it's basically exactly like the OEM setup. Just make sure you get the polarities right, obviously. I ended up not needing the 48V step down to 12V for the lights since that was already built into the Club Car electronics. Returned that to Amazon. I used the same battery monitor linked and same set of cables linked (except bought the variant for Club Car instead). The cost was about $1250, $1100 of which was just buying the batteries. The conversion took about 1.5 hours for me and my electrician uncle, neither of us had really done something like this before.
Couple of notes:
48V draws less current than 36V. The BMS on those batteries is rated to 100A. Starting from a complete stop and flooring it at the bottom of a steep hill spiked the draw to 150A but sustained around 105A. Never had any issues with the BMS shutting the batteries off in my tests. It might be theoretically possible to use 50Ah batteries because of the higher voltage but seems sketchy.
The battery monitor is great and 100% worth it. It needs a discharge curve to properly set it up but those can be looked up online e.g. https://footprinthero.com/lifepo4-battery-voltage-charts
So overall, to do this one needs
And optionally