“found in several calculators but this specific one was from an SR7949D (only sold in the UK)”
The two GHU chips are made of a (high silicate?) epoxy I've never seen before. The silicate content makes chemically decapping them extremely difficult. Although I can get acid to penetrate a few mm to remove the epoxy it leaves a strong skeleton behind that so far I've only been able to remove mechanically. So this is where they stand: GHU-01A: was dipped in hot acid for a few hours (contrast to minutes for the other chips) to take out a lot of the epoxy. I haven't done any further processing on it, looks like this if you are curious (picture below) I may be able to mechanically lap it to expose the chip surface but this will be somewhat labor intensive (same with above if I got another copy)...