The only easy way i found to align my delta Bed, to be 100% this should be position below the towers, but it was impossible for me so i design this solution and is working very well, you can adjust the alignment space you need depending on the size of the spring, i did cut my springs very small so i can have 2 to 3mm max to play with alignment.

This was design to be use in V-slots 20x20.

The only thing you may need that i don't show on pictures is an extra nut, to be place below the hotbed to tight the screw, to avoid the alignment screw to twist.

The twist button, have space to have a M3 locking nut if you prefer, for what i test it works with regular nut without any problem

Material you will need:
3 x M3 Countersunk head screw (+- 16mm) alignment screw
6 x M3 Countersunk head screw (+- 12mm) attach the part to the frame
3 x M3 Nuts
12 x M3 washer
3 x small hard springs ( i did have some springs that i did cut to the size i need, don't use soft springs )

Tip: I did use superglue to glue the nut and washers to the twist button, to help me on assembly.