I seriously think not. RT is really disinterested in the inboard diesel engines for both the R-23 and the new 2018 R-27. It maybe that RT will do the stern drive for the R-23 still but for the new 2018 R-27 I believe you will be out of luck.
I asked Livingston (owner/designer) of the RT models about the stern drive for the new 2018 R-27 and his reply was "we looked at doing it early on, but have abandoned that." With this in mind the new 2018 R-27 (early models at least)have a hatch molding at the forward center of the cockpit floor, close to the cabin door entrance. This was going to be the cutout for a round hatch to provide access to the diesel stern drive's fuel tank line and shut off valve. I suspect the hatch molding will not be evident on some future new 2018 R-27s as the stern drive option has been abandoned permanently AFAIK.
If you want the R-27 (Classic) with its inboard diesel you will either have to find a new or used one at a dealership or else where as RT has at this time stopped assembling these R-27s at their factory. They could/may restart production for this R-27 model line if sufficient demand for it materializes. 😉 ... but of course, I'm not privy to Ranger Tugs ultimate decision on whether to continue with the R-27 (Classic) production. But if you ask me, the R-27 (Classic) will follow the same path as for the R-25 (Classic). It could be that the R-25SC will be abandoned as well, as the R-23 could be viewed as its replacement by Ranger Tugs in a short while. The remaining diesel power Ranger Tugs are likely to be the R-21EC, R-29, R-31 and possibly a new R-38.