Say you want an 50 degree overlap advertised and 4 degrees @ 0.050" with a 105 lsa, I'm sure you just add half of overlap to lsa and x 2 for duration.
50/2 = 25 + 105 x 2 = 260 advertised and 4/2 = 2 +105 x 2 = 214 @ 0.050"
Edit* just 2 x lsa + overlap = duration guess is easier :) eg.. 2 x 105 + 50 = 260, 2 x 105 + 4 =214.
And if you want a split cam both have to add up to total duration of both intake and exhaust of a single pattern eg.. 520 (2x260) eg.. so 256/264 on 105 lsa etc..
Pretty sure that's right, maybe someone will verify :)