I've never had saladitos, but that sounds good. I make umeboshi, so I would just follow the same procedure/ guidelines (see below).
The fruit should be unripe* (green and hard, but full size) and blemish free. Soak the fruit for 3 hours to overnight ( the internet doesn't seem to agree so follow your heart), fully submerged in cool (plain) water (use weights/ plastic bag of water to keep them under).
After soaking, pick out any woody bits left in the stem end with a skewer. Pat fruit dry. Weigh fruit (in grams, makes the math easier). Weigh out salt at a 20% ratio (20g salt for every 100g fruit); you can go as low as 18%, but no lower. I do 20%.
Sterilize your crock or jar with strong alcohol (I use vodka, but anything high proof will work). Sprinkle a light layer of the pre-measured salt on the bottom. Arrange a layer of fruit on top of it. You don't want them all smashed down like kraut, but a little snug together is okay. Sprinkle a layer of salt, add another layer of fruit. Continue until you run out, making sure there's some salt left to sprinkle on the top. Use a (sterilized) plate or sheet of parchment paper to completely cover the top of the fruit (this is for a huge batch; if doing like a quart or 1/2 gallon jar, then just the weights themselves are enough to keep the fruit from being exposed to air).
Add weight to gently press the fruit (not more than 2x the weight of the fruit or the skins could split). Cover with a lid (if your vessel has one), or use plastic wrap (or oilcloth, I guess, if you're anti-plastic, maybe even a dried pig's bladder if you really want to get authentic) to seal everything up--you don't want mold spores getting in there. Store in a dark, cool (-ish, since I do mine in early summer, ambient temp is usually in the mid-low70s F in the cabinet where I keep them). Keep a record of the start date, preferably right on the container.
Let them sit for a week before opening them to check progress (though if you're using glass you can look at them whenever you want). By this time, the plums should all be submerged in their natural brine. If they aren't, you can gently rearrange them with clean hands/ utensils and put the weight back on. This is also the time to add the shiso, if you're using it. Let them sit another month (or longer, sometimes life happens and I had no issue with the jar I let sit for almost 2 months). When finished, drain the brine/ vinegar and save that in the fridge as an awesome condiment; dry the fruit using your favorite method (sun-drying over the course of 3 days is traditional for umeboshi, but I just use the dehydrator set low/ ~115F and it's fine).
I'm thinking that you could probably mix chili flakes into the salt to flavor the apricots, kind of like adding the shiso to umeboshi. If I can get some apricots this year (the last few years have been bad and there was crop failure at every orchard in a 25 mile radius of me), I'll have to try it.
*This is for umeboshi and sour peach pickles (I forget what they're called). For something sweeter, ripe fruit is probably okay, but has a higher chance of the skin splitting. If using ripe fruit, I'd skip soaking and just wash them well.