After getting the last part I needed I fitted my 4 to 5 speed conversion from Brommie+ last night to my P-Line.
As well as the kit from Brommie+ I used a deore M5100 cassette to get 11-13-15-19-21 cogs and an XTR 11-spd chain. I reused the lock ring from the original 4-speed cassette as it’s a little slimmer than the deore one, but I think either would have worked.
I couldn’t find much online about chain length for this setup, I have a 50T chainring and figured I’d need to add at least 1 link to the chain. However I found that initially although the gears shifted OK, in the 11T gear the chain would slip off the derailleur pulley and jam. I tried to adjust the limit screw but it didn’t help. It wasn’t until I went back to the original chain length I found this problem went away, so if you’re struggling getting this setup- check your chain length!
by Mundane-Season-4911