Besides the Furuno GT-8036 breakout board, I just did a layout for a board that converts the pinouts of Motorola M12+ compatible receivers to a 0.1" 9-pin header that (mostly) matches the Adafruit Ultimate GPS. The Adafruit ENABLE pin is repurposed as a DGPS RTCM corrections input and the Adafurit +3.3VREG output pin is used to provide external antenna (5V) power... the board defaults to use the 3.3V VCC power input for the antenna power. Contact me off list if interested.