Post Whipple so must take antacids and enzymes. Guidance says avoid calcium carbonate and magnesium hydroxide antacids. Any alternatives please?

Alternatives. The problem is most antacids are from the 2 chemicals but you can use Gaviscon which is a little different and so could be used without over use. However I do not know if you can use meds or are on the H2 receptor blockers (Zantac, Pepcid, (famotidine) Axid) These can help with the heartburn as well. You can try these and see. I hope it is some help but depends on your provider.
Why Whipple? You must have an intense relationship with several Drs after such difficult surgery. Ask your Drs every single question. Write them down to help you remember when you go. Do not attempt to figure anything on your own.