SDNG would require light PCT, shutdown is minimal. And with people resonding differently to different things, why take the chance? AX's aPCT was created for just this purpose.
And you would be fine to take Retain2 while taking SDNG and afterwards. Stacking the two with MassFX would make a killer combo. I'd do 4 weeks of SDNG, MFX, R2 followed by 4 weeks of aPCT & R2.