The TA reading is a true reading of Total Alkalinity (TA). However, for calculating the Calcite (sometimes called Langelier) Saturation Index, one needs to adjust the TA by the a fraction of the CYA amount in order to get the carbonate alkalinity. All of this is done automatically for you if you use The Pool Calculator. You want your saturation index to be near 0 for a plaster pool. It just means that the water is saturated with calcium carbonate to protect plaster (which contains calcium carbonate) from dissolving or from forming scale. With a quality plaster job, you don't have to be that close to 0 in the index.

Of course, the bigger issue is your having a CYA that is too high. It will be harder for you to prevent algae growth using chlorine alone unless you use a very high FC level and if you run into trouble the shock level of chlorine will be impractical. It would be better for you to do a partial drain/refill to lower your CYA level and then follow the Best Guess Swimming Pool Chlorine Chart.