Updated:
Increased overall length and tweaked the mounting holes a little bit to have a tighter fit, still not final yet and more updates to come im sure.
Need help indexing your round build plate on your FLsun V400? Try this and let me know how it is, let me know in the comments if any updates need to happen. I will also be updating the pictures when i am able to test fit it to the printer. I left some space in between the bed indexer and the upright frame it attaches to so you could use a cover for the upright to keep loose filament or whatever from getting into the printer, i Personally used these from phnxdrgn536 and they came out great, a little tight but they work well.
https://www.printables.com/model/341276-flsun-v400-pillar-base-cover
The preferred material to print this in is ABS/ASA because it is going to be subject to a fair amount of heat, but if you only print in PLA then you could probably get away with PETG. It also requires a little bit of support on the round raised side, but its not too much.
This was created in tinkercad so there are no step files to give out, sorry.
The only hardware needed is:
2: M5x10mm bolts
2: M5 T/Hammer nuts
The author marked this model as their own original creation.