I've got a working JSON endpoint for you to test out:
Set a header 'X-HTTP-Token' to 0a749982cf816b830035dd69adebe537e5694fb9
nextCursorMark is returned in the response and can be set as a request param (as "cursormark"), in addition to rows (as "rows"). Rows defaults to 1000.
Nicole has a document detailing the DLG fields here.
I've thrown this together pretty quickly but all my testing looks good.
Have a nice weekend, y'all!