The engine will tell you what viscosity it likes by its hot oil pressure. If clearances are not much greater than stock 10W30 should be fine.

Your flat tappet will want more zinc than current car 10W30. I don't know the zinc content of the oil you've choosen. I do know diesel engine oil has a good amount - even the newer grades - so my choice would be 10W30 Rotella T. Some additional zinc for break in would help too (STP, GM break in supplement, Comp Cams break in supplement ect.).