Pixhawk with redundant magnetic compass

I think I’ve had success last night with adding an extra magnetometer to my current pixhawk APM setup.
It was an Osepp mag, a relatively cheap unit but has the Honeywell sensor chip, and a nice I2C locking interface plug + a matching ‘chain port’ for more I2C devices in serial.
The 1st one I tried did some funky stuff in calibration…wouldn’t show dots anywhere near equatorial areas in the calibrator 3d graphic…
So I had another mag, same exact type from last years arduino experiments, and it calibrated perfectly 1st try. I made a small expansion box with a rugged 4 pin plug for I2C and a 4 wire cable with braided sheild thats about 10 inches long.
I will attempt the same with a spare GPS next, but there is no resident I2C format interface on the unit to be added… just a Vin, Ground, Tx, and Rx terminal.
My task today is to find a circuit for level conversion of that SPI signal to I2C.
Not sure if its even needed if signal can be lowered to around 3v.
Anyone know any tips on this?
Will update when I get to next juncture.

Hi - any updates?

Thanks, Grant.