Acid whey substitute for Latvian rye?

I'm interested in making this recipe for a Latvian rye bread:

https://crucide.livejournal.com/130434.html

The recipe calls for whey, which I assume to be acid whey. I know I can buy some regular yogurt and strain it to get the acid whey and Greek yogurt. However, I only have Greek yogurt because I buy it at Aldi (but made in a Chobani plant) for $3.50/32 oz and avoid the hassle. Therefore, I am looking for a substitute for acid whey using materials I already have on hand:

I have the following:

• Sweet whey powder
• SACO Buttermilk powder (cultured blend of sweet cream churned buttermilk, sweet dairy whey, and lactic acid)
• 88% Lactic acid

Acid whey and sweet whey have similar compositions, the major differences are the calcium content and total acidity:

I can prepare a solution (suspension?) of sweet whey at 5.6 wt.% and adjust the total acidity to ≈73 mM with lactic acid. I could also add some calcium carbonate to approximate the Ca content and provide some buffer to the solution.

Any feedback or other ideas (straining yogurt is a last resort) are welcome. 

Thanks!