Nice score! I have one too and it's one of the bikes I won't ever give up. Keep us posted as you work on it.
I do see a few differences, like the shifters, seatpost, and the crank. I always assume mine is correct but who knows? When I got mine I thought the only thing not original was the saddle and wheels. I do still want to source some quality tubulars for this one day.
Here's how mine sits for now. The original cloth bar tape is still under the new leather wrap. The hoods are replacements too as mine were falling all apart.
Here's a photo gallery of mine in case you need something to reference as you sort it out.
https://pbase.com/jhuddle/opus_iii