Some simple, desirable experiments to perform
There are a number of obvious experiments which would be very desirable to perform. I have not yet performed them myself only because I am extremely satisfied with my current dietary situation, and, after almost nine years of absolutely continuous, strictly regimented, dietary experimentation, am not presently seeking further self-experimentation. However, if any atrial fibrillation sufferer found benefit with the techniques described but, for example, found large amounts of cranberries too much in the long run, they could investigate some of the following possibilities and compare the results. (And hopefully report them somewhere!)
Some obvious experiments (while keeping calcium and vitamin D constant) are:
Substitute the 500 grams of cranberries for two weeks with 3.5 grams of quinic acid per day. This is available as a pharmaceutical-grade product from at least Buchler GmbH in Germany. 3.5 grams is approximately the amount contained in 500 grams of cranberries .
Substitute the 500 grams of cranberries for two weeks with 250 grams of prunes per day. This is approximately the amount of prunes which was said to give an equal acidifying effect . However, whether a modern prune is the same as a 1923 prune, and has the same quinic acid content, may be an open question. It is my perception that readily available plums have been widely “improved”, even in recent decades, and are typically considerably less bitter than recalled from earlier years. It seems likely that this has happened across most varieties, including prunes, of such a major commercial fruit as the plum.
Based on the discussion here (Link H), regarding other possible active components of cranberries such as resveratrol, OPC’s and ursolic acid, substitute the 500 grams of cranberries for two weeks with 0.5 mg of resveratrol, which is readily available from supplement suppliers. This may be approximately the amount contained in 500 grams of cranberries [3,4]. However, since good analyses of whole-cranberry resveratrol content are not readily available, and since the US allows the routine sale of resveratrol as a safe supplement in single doses far exceeding 0.5 mg (eg 500 mg per capsule) it would be easy, and probably desirable as a test, to experiment with a dose much higher than 0.5mg per day for two weeks.
High-potency, concentrated supplements of oligomeric proanthocyanidins (OPC’s), and also of ursolic acid, are also readily available, so similar experiments could easily be performed on these possible active components also.
These would provide extremely convenient alternatives if proven to be as effective as whole cranberries.
Another possibility would be to try, for example, quinces or crabapples. Malic and quinic acids, totalled together, are reported to comprise around 98% of all acid in quince fruit pulp, and, from the only published chromatogram (graph) in the same study, it seems that quinic acid may be nearly half of this amount . But this is not absolutely clear. Quinic acid compounds are also reported to be the second most abundant acids in some ciders and cider apples  (understandable, because many of these are more sour and bitter than table apples -- see explanation here -- Link G), and are also referred to in crabapples (are they even more abundant in this more wild-type ancestor fruit?) and even in unripe table apples. But, in all these cases, some estimates would need to be made of cranberry-equivalent amounts, and there is no obvious benefit to long-term use of these fruits in preference to cranberries -- I am merely mentioning the reasonable possibility of the existence of other effective “wild-type”, or even unripe modern fruits (see related discussion here -- Link G). The threshold for an “unripe” fruit would have been very different in the era when humans were consuming only wild fruits in competition with each other and with many other creatures.
Cranberry juice, although much lower in total nutrients than whole cranberries, would presumably be effective. But it would not convey much information as an experiment.
 Fellers, C. R., Redmon, B. C., & Parrott, E. M. (1933). Effect of cranberries on urinary acidity and blood alkali reserve. The Journal of Nutrition, 6(5), 455-463.
 Blatherwick, N. R., & Long, M. L. (1923). Studies of urinary acidity II. The increased acidity produced by eating prunes and cranberries. Journal of biological chemistry, 57(3), 815-818.
 Wang, Y., Catana, F., Yang, Y., Roderick, R., & van Breemen, R. B. (2002). An LC-MS method for analyzing total resveratrol in grape juice, cranberry juice, and in wine. Journal of Agricultural and Food Chemistry, 50(3), 431-435.
 Rimando, A. M., Kalt, W., Magee, J. B., Dewey, J., & Ballington, J. R. (2004). Resveratrol, pterostilbene, and piceatannol in vaccinium berries. Journal of agricultural and food chemistry, 52(15), 4713-4719.
 Silva, B. M., Andrade, P. B., Mendes, G. C., Seabra, R. M., & Ferreira, M. A. (2002). Study of the organic acids composition of quince (Cydonia oblonga Miller) fruit and jam. Journal of Agricultural and Food Chemistry, 50(8), 2313-2317.
 Whiting, G. C., & Coggins, R. A. (1975). Estimation of the monomeric phenolics of ciders. Journal of the Science of Food and Agriculture, 26(12), 1833-1838.