An AMBEserver installation made on a Pi3 will not work on a Pi2 or Pi1 without modifications. This is because of changes to config.txt that are different and the serial port difference. This may be able to be fixed.
The enable_uart=1 line should be able to be used on both platforms, so it's safe to put in there unconditionally. enable_uart=1 is default for Pi1/2. It's only optional for Pi3.
The init_uart_clock setting is increased greatly to support the bluetooth on Pi3. We should be able to put this parameter in by hand and see if it still works on Pi1/2. It may be that with new firmware this is already done. It should be investigated.
With the new Conflicts line in the systemd unit files, starting AMBEserver on one of those ports is going to start getty instead if it fails. We should explore seeing if we can block the bluetooth daemon (hciuart) too and just enable both ttyAMA0 and ttyS0 on all Pi platforms.