Being firmly rooted in Africa[...] Afro-Peruvian music has no clave, the underlying five beat pattern in much Afro-Cuban and Afro-Caribbean music. Instead the styles within Afro-Peruvian music have many variations but, like the African-rooted American jazz music, no clave.
And with a looser structure:
It's not a rule that you have to play festejos exactly the same every time. It has many, many, many variants just as there are variants of swing patterns in a ride cymbal for a [jazz] drummer.
The music was originally played just with a percussion section, but seems very friendly to the use of the drumset— at least in a “modern”/commercial/jazz-oriented format. The ostinato on this page is pilfered directly from a video by David Cornejo, a Peruvian drummer living in New York, and the left hand independence parts are stock rhythms useful for improvising with other forms of this “Afro 6/8” family of playing. You'll also want to pull Cornejo's left hand rhythms from his video below— and check out his other stuff; he has a YouTube channel with a bunch of good videos.
Play the left hand part as a rim click, then drill the entire page using my standard left hand moves, varying the accents and timbre. I would also learn the page in a duple, 6/4 meter— with a quarter note pulse, so the cymbal rhythm would be counted 1&-&3, 4&-&6.
Get the pdf
Here's a link to the Alex Acuña track he's playing along with. Search “Afro-Peruvian”, “Peru negro”, or “festejo” on YouTube for more.