My experience with muratic acid and my 325 gal. tub tells me .4 oz will not do enough for you in the long run. Your PH might initially drop to 7.6, but it will climb again in short order.
A better approach might be to drop TA in increments and see where PH stabilizes.
If you look at the bottom of the Pool Calculator page you will find an 'Effects of adding chemicals' paragraph. This app. contradicts the calculator section somewhat in that it shows a .57 drop in PH with 1 oz of muratic acid added to your tub. The TA drop looks accurate for you and that is where I would focus, if I were you.
Add the oz., check TA to confirm drop accuracy, then check PH and PH again tomorrow. Keep this pattern up until your PH stays where you want it.
For what it's worth, my tub likes: TA 60, CH 200, CYA 25, Borates 50, Temp 100. This gives me a saturation index of -0.14 but keeps my PH rock solid at 7.6