I think you're on the right track thinking the cams are retarded.
Based on that the simple option is to advance both. The really time consuming bit comes in when you start to change the overlap by only advancing, or retarding one cam.
It is a tricky one, the more time you spend the better it should get.
I can't remember what ecu you are using. I found using an AFM would mean mixtures wouldn't need touching, so could be done on the road, or heaps quicker on the Dyno. Where a map ecu would need tweaking to keep the mixtures nice due to changing the volumetric efficiency.
I haven't come across the info required to dial in stock cams, and as I have previously mentioned to you when I dialed in my type b cams found they were 4 degrees out. So stock ones would be the same, the thing is its either 4 advanced or retarded. Could be why some 30 builds seem to have super response, running the cams 4 degrees advanced from stock settings, and extra capacity. Considering guys have messed up timing belt installs and run multiple teeth out with the engine still making decent power, it goes to show cam timing issues can be ignored (not that they should, it just doesn't mean the engine doesn't work)
Hope that makes sense.....
Tl;dr
Advance both cams.