If we assume the navigation board (GPS I assume) draws no nore than 1A at 3.3V, the LD1117xx-33 will be a sufficient linear regulator. You will need a 10uF 6V electro at the input and at least a 100uF 4V electro on the output. These should be mounted closeby and have short leads to prevent oscillation. The regulator also needs to mounted to a metal heatsink to remove the heat it has to get rid off, otherwise it will die.

So looking at the LD1117 TO-220 package, with the plastic square bit in front of the metal tab which is at the back, pin 1 is the leftmost pin, and pin 3 is the rightmost pin. Unfortunately that stupid Chinese datasheet doesn't tell you what pins 1,2,3 actually are. Another datasheet shows that pin 1 is ground, 2 is output and 3 is input.

This regultor will continue to draw up to 10mA itself, without any 3.3V nav board load (so it will eventually discharge the battery by itself).

2. The I2C Signalling

Unfortuantely you need to add additional level-shifters to make the Nav board play well with others on the I2C bus. These can be simple transistors on the SDA and SCL lines or a dedicated open-drain (not totem-pole) logic chip. The NPN transistors can have their bases fed through a 10k resistor, their emitters tied to ground and their collectors tied to the appropriate bus line. Or you could use N-channel JFETs or depletion-mode MOSFETs. Plenty of options, but an active (not resistive) level-shifter is necessary.

^{_{So long, and thanks for all the fish.}}