Quote:

On our 4.25 stroke / 6.535 / 4.5 bore the bottom of the pin bosses hit the crank throws also. Dont forget to check that.

I run that combo in my KB block. Discuss this with the piston manufacturer when custom ordering. I have seen the thickness under the pin (on the boss) from 0.150 to 0.230" depending on application.

Here is the math for that one.
CWmax = Counter Weight max dia
Pthick= Piston thickness below the pin
Pin = Piston pin dia
Rod = Rod Length

CWmax = 2(Rod - Stroke/2 - Pin/2 - Pthick - Clearance)
For example:

CWmax = 2(6.535 - 4.25/2 - 0.990/2 - 0.190 - 0.125)
CWmax = 2(6.535 - 2.125 - 0.495 - 0.190 - 0.125 )
CWmax = 7.20" dia
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If you are OK with 0.060" clearance and want 4.44 stroke:
CWmax = 2(6.535 - 4.44/2 - 0.990/2 - 0.190 - 0.060)
CWmax = 2(6.535 - 2.22 - 0.495 - 0.190 - 0.060 )
CWmax = 7.14" dia
If you need more thickness under the pin (on the piston) you will need smaller crank counterweights and maybe heavy metal slugs to balance. For those longer strokes, you could use a longer rod and very short piston compression height.