http://www.g4jnt.com/PIC_Opera_Source.pdf
http://www.g4jnt.com/OperaBeacon.zip

PIC16F628A (although will easily fit into a 16F627A)
Link selectable for the four speeds and 8 duty cycle settings.
Active-low key line and Tx enable.

Use the 'PIC' option in the   Opera.exe   software to generate the 225
 bit  '0' / '1'  pattern for your callsign.
Copy and paste to a text file and run the conversion utility to format
for PIC assembler.
Reassemble the source code, programme the PIC and enjoy...

When copying the bit pattern from Opera.exe, note that the "Copy"
button doesn't seem to do anything.  You will have to use the standard
right click and copy-to-clipboard procedure.

I've tested by keying an audio tone at 2, 8 and 15 minute speeds and
getting correct decodes (you may have seen the reports during code
development & test phase earlier today).   I couldn't be bothered
doing a full 31 minute test.

Andy
G4JNT