Not tax advice, but I believe you would just need to calculate...

Not tax advice, but I believe you would just need to calculate the cost base of your new RMS shares.

https://www.ato.gov.au/Forms/Guide-to-capital-gains-tax-2022/?=redirected_CGTexemptionsandrollovers&anchor=Exemptions_and_rollovers#Scripforscrip

Scrip for scrip

You may be able to defer a capital gain if you dispose of your shares in a company or interest in a trust as a result of a takeover, see Investments in shares and units.

https://www.ato.gov.au/Forms/Guide-to-capital-gains-tax-2022/?anchor=Scrip_for_scrip_rollover#Scrip_for_scrip_rollover

Scrip for scrip rollover

If a company in which you owned shares was taken over and you received new shares in the takeover company, you may be entitled to a scrip for scrip rollover....

A rollover is only available if the exchange is in consequence of an arrangement that results in the acquiring entity (or the wholly owned group of which it is a member) becoming the owner of 80% or more of the original company or trust.