I’ve installed a cam, and D.D.’s book shows .010 intake, and .020 exhaust. The cam card, however, shows .010 and .012 SO, which should I go with?

Cam card.

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010 & .020 are factory cam lash specs. but other cam profiles can have different lash settings.
What cam do you have?
DD

It’s a Comp Cams .220/.220

D

And doing it cold,with new valve train I figured to add .001 to get it decent for startup and break in. Surely it will tighten up a bit when hot, and loosen a bit when everything seats. Then supposed to start right away and run at 2000rpm for a half hour..THAT will be hard for me, it’s “against my nature”..

Vote # 2 that that Comp grind will likely run better with looser lash.

Me,... I would start with .012 In / .016 Ex static adjustment (EOIC method) to start the engine.
Run the engine between 1000 and 1800 RPM,. (seeing that the SL6 cam is sitting right next to the crankshaft, it will get lots of oil "splash")
Be sure all the push rods are spinning and check / tighten any loud ticking valves.
Stabilize the engine and then bring down the RPMs and do a hot & running lash adjustment.
See how loose you can go on the lash, before getting a ticking sound..
I often run Comp Cams with .016 lash clearance on the exhaust valves
DD.