If you have OEM lifters you will have some trouble getting them out without
dropping them in your pan, which is normally OK but CAN cause severe problems
if they don't drop ALL the way into the pan. In some cases they can be hit
in an intermediate position and damage internal parts, like rodcap bolts, or
maybe even exit the crankcase in a worst-case scenario. Usually they are
mushroomed somewhat on the bottom and very difficult to pull out the top.
After pulling the cam you may be able to put some kinda semi-flexible trough
through the cam bore and catch them but they are long enough that a stiff
trough will not allow them to completely exit their bore. My best catch record
has been 7 lifters out of 12 on a B30, all of whose cam journals are
big. With the B20, which has smaller journals in the back, it is even harder.
I had one in my 73 164 that dropped into some intermediate location and got hit
by the #2 big end in the first 10 miles of driving. Made a sickening clank on
a hard turn followed by normal operation. Not being in a position to do a
teardown, I went ahead on and drove the car across the country a couple times
and on the third trip it started acting strange headed east from Yuma, really
strange by Tucson and just BARELY made it to San Simón, Arizona. Later we
determined that it was just short of throwing a rod and it had about 1/4" slop
in the #2 rod big end, apparently because one nut was broken off the rodcap and
it was opening up, with the piston banging the head.
So, as I say, NORMALLY it's no problem but the exceptions can really get you.
I was stranded with wife and teenage daughter at San Simón, AZ. We hitched a
ride in a pickup to Road Forks, NM where we spent the night, back to San Simón
the next morning, and finally talked the guy into taking us to Lordsburg, NM
with all our stuff the next day so we could take a Greyhound to El Paso where
we could rent a car to get on to Tennessee and Charleston, SC. The one-way
car rent was $175, but it had some GOLDEN virtues:
1. The air conditioning worked WELL
2. It used about half the gas of the 164
3. If there was a problem with the car it was NOT MY problem!!

Best way to determine amount to mill is by combustion chamber volume,
although 0.040" usually is a good average. Mike the head thickness first
to make sure somebody didn't beat you to it.
You cannot safely calculate CR from compression test pressure because of
variations due to wear, valve leakage and most of all, valve timing.
--
George Downs Bartlesville, Heart of the USA!