I'm doing a cam swap and took some measurements of the lobe base circle while both cams were on the workbench:

TR224: 1.439"
LS6: 1.498"

It makes perfect sense that 0.025" longer pushrods are needed in order to maintain proper lifter preload w/ this cam, the radius difference is 0.0295".

Hope this helps somebody down the road.

 

I measured my stock cam and a tr224 a long time ago, and I came up with something like 1.445 for the TR, and 1.450 for the stocker, indicating they are 0.050 different. So the pushrod sees half of this, .025. Meaning, like stated, a .025 longer pushrod is warranted to maintain factory preload specs. However, with the more aggressive lobes of after-market cams, slightly less preload may be a good thing.