Its probably best to ask a maintenance shop that is certified to maintain 421s or B58s. At least Cessna had a huge SB, that costs a lot of money, looming. Had to do with corrosion IIRC.
Anyway, maintenance programs do change and if someone knows these numbers, it should be a maintenance organistion.
And have alook here:
www.comlaw.gov.au/Details/F2006B08327/316ed830-525c-434f-ad31-306e63298772