please see this document :>

https://www.sdr-kits.net/documents/PA0KLT_Manual.pdf

and look at fig. 7 on page 13/21 for impedance / transformer connections.

I am using the Si570 as a VFO for my airband AM receiver too with good results. I did try it last week !
Used also for : Two meters FM receiver and for APT (137 MHz ) 40 KHz IF FM receiver.
all the best !
73, iw2fvo
Ambrogio