6.1 cam swap. Big deal?

no. they move. the chain markings are an additional help when you remove the sprockets and put them back. that shows nothing moved like when you clamped sprocket and chain together. especially when you have no clear marks like here. In europe I am used to have dots on the sprockets and on the body. never seen markings on the chain. The chain can go in any position.
anyway, i put the 2 o'clock and 12 o'clock position. engine turn free with the starter. Now i'm waiting for the valve spring locators to install and fire it up.
I don't want that before everything is 100% correct. because of those tight valve to piston clearance now