You might want to remove the valve covers,
set up one dial indicator centered on the rocker arm tip directly over the center of the valve stem,
and another dial indicator on the other end of the rocker arm directly over the center of the push rod
and actually check what 'real world' ratio
your factory Magnum rocker arms truly are.

A few years ago Jesse Lackman of RevSearch posted here on Moparts that he did this and found that the actual ratio was closer to 1.7 than the 'nominal' 1.60 ratio.

In one of the three part "Magnum Manifesto" articles in Sept 1998 in Hot Rod Magazine they also list the factory Magnum rocker arm ratio as greater than 1.60

repost of what Lackman wrote back then:
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Jesse Lackman
Moparts Member
Posts: 395
From: Center, ND 58530
Registered: Jan 2000
posted 07-13-2002 05:16 PM
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how about 1.74?
Just measured one with a dial indicator. lobe lift at the rocker pushrod
socket = .345"

valve lift at retainer = .600"

Did it about four times to make sure

Jesse Lackman
Moparts Member
Posts: 395
From: Center, ND 58530
Registered: Jan 2000
posted 07-13-2002 10:52 PM
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I did check another one came up with a little less but still over 1.7.
Hughes has lots of roller cams for the magnum engines.


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boxcar
Moparts Member
Posts: 151
From: Mason MI USA
Registered: Mar 2001
posted 07-13-2002 10:07 PM
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Yeah, suprize! When I was degreeing in the cam in a magnum engine I got to
checking things and the ratio I got was around 1.69.

Made a cam lobe that was 270* seat, 218* @ .050 at the pushrod check at 224* @
.050 at the retainer. Makes you want to run out and spend $400.00 on some
heavily marketed roller rockers, NOT.