Take a look at the attached 'Bearing Clearance & Oil Viscosity Recommendation' chart from Driven.

They appear to be pretty spot-on, and at least in my case with mains (360 crank) at 0.0033 clearance and rods at 0.0022 I am going to run 10W-40. Now these recommendations are applicable to regular use as opposed to break-in, however I would say the viscosity stays the same while the ZDDP content of your oil needs to be a tad higher to give the FT cam a better chance of breaking in correctly.

Since that 20w50 you have is a break-in oil already I would imagine the ZDDP is high enough, good to check though.

I would be a little worried that it may be too thick though, especially at start-up when you want oiling to happen as quickly as possible...so maybe mix it 50%:50% with something like 10w40?