http://cbastro.org/results/highlights/iyuma-b/iyuma.pdf
The above reference was the only one I've come across which shows the spectra of a CV from 450nm through to 740nm. This one is IY UMa, but I would have expected some similarities.
Figure 14 Shows the Hb emission with a central trough ( also the Ha),
HeI absorptions at 4921, 5015, 5876, 6678, 7065
and another (?) emission at 5861.
Trying to match any of these to the OY Car spectra is very difficult.
If we assume the large hump shown at around 4750 is Hbeta(4861) , then the next two emission "bumps" seem to match the IY UMa data (??) and the hump at 6710 is Halpha (6563). Based on the Balmer series the strength of the Ha should be twice the Hb so it doesn't look right???
I think we need a higher resolution spectra to be able to go much further.
An excellent example to "practise" with!!!! Well done.