guit99

Yes use the RW RP in the neck and Pos 4 will be humbucking. If you use the RW RP in the middle like you do with a 3 single set up and split the bridge pickup in pos 2 then that WILL NOT be humbucking but if you use the RW RP in the neckand the standard wind in the middle both pos 2 amd 4 will be humbucking. Im running the stock 500 K Washburnn pots in all my MG guitars.

Welcome to the forum! Owned a number of these guitars have a total of 5 USA MG's now so do know them well.
I ran a set of Dimarzio Blue Velvets in my 1st ash body MG 100 with a Duncan Crazy 8 in the bridge and have used both Duncan SSL-1's and Alnico II pros in these with success. Like you I find the SSL-5 to hot and dark in the neck and middle although I do like that pickup in the bridge on a strat. You want to use the RW/RP in the NECK position not the middle if you plan to split the humbucker in the bridge and have in hum cancel.
Right now I have a pair of SSL-1's in my 95 MG 120 with a JB in the bridge that is set to auto split in pos 2 of the 5 way. Combo works really well in that guitar