MAX1472 Source impedance
The data sheet says the optimum loading at the output of the PA is between 100 and 150 ohms with a 2.7V supply (page 6).


  The output-matching network suppresses the carrier harmonics
  and transforms the antenna impedance to an
  optimal impedance at PAOUT (pin 4), which is between
  100Ω and 150Ω for a 2.7V supply.


So aim for something like 125 ohms.

Matching networks are frequency sensitive. 

The misleadingly-named Application Note 1954 "Designing Output-Matching Networks for the MAX1472 ASK Transmitter" presents several pre-designed networks for matching to a 50\$\Omega\$ antenna at frequently-used frequencies.