Stamp Me! Letterbox Hybrid

AS OF 8/21/21 ALL OF MY CACHES WILL BE UP FOR ADOPTION, IF YOU LIVE IN THE AREA AND ARE AN EXPERIENCED CACHER PLEASE MESSAGE ME!!!

I have a one-of-a-kind custom stamp, which means YOU CAN ONLY GET IT ON THIS HUNT! This is a multi-stage letterbox cache, so you will be walking the Cross Island trail to retrieve the cache, so if you figure out the final location you can just drive there. There's a parking lot where I've placed this virtual waypoint. But the local government has just constructed the finishing touches on the trail, in this case, I suggest you take the walk since it is quite lovely. The container is large enough to place tradeable and TB's inside. Even if you don't have a stamp log, you can still retrieve this cache and have fun with the goodies inside. 
 

To find the cache you must find the last 5 digits of the coordinates:

North: Mpmaf-Lpnoa . Mvby Mpcl Mvby

West: Mpmallu . Zlclu Upul Mpcl

Have fun! Please close up the ink pad after use!

You can check your answers for this puzzle on GeoChecker.com.