got ahead of myself- installed all rocker arms
 

I am following Wayne's Book for my 1973.5 911 Targa (CIS) but jumped the gun and installed all the rocker arms before timing the cams. Just goes to show you should read an entire chapter before proceeding to potentially waste a good amount of work.

Do I have to remove them all (except for 1 and 4 Intake) or can timing be done with all of the rocker arms installed?

Set 1 and 4 valve lash and time the cams. There is just more resistance to setting the timing.
Bruce

I found that the the extra resistance held the cams in place better.

i always do it that way. it keeps the cam in position way better than just one.

I did a test-run cam-timing during disassembly to see if it was as hard to do as some people make it out to be - turns out it was a pretty straightforward operation. The timing was retarded by a number of degrees and (with all rockers installed) I was able to set the timing right on the number in two tries on each side.

During assembly, with just the #1 and #4 intake rockers installed, it took me all night to get the timing right. Indeed, with all rockers installed, the cam is held in place as you remove the pins and make those little sprocket movements. That's how I'm going to do this next time (if there is a next time...)

GK

+1

Just be sure to leave the other cylinders (2,3,5,6) & 1 & 4 exhaust valve lashes loose! The Motronic (and I assume CIS also) pistons have a small window of timing where everything fits, if you're outside that and try to turn the engine you might get valve - piston contact.