Starter will not turn motor

[gnarlycreature]

Hey guys, I've been finishing someone else's project I purchased two years ago. I'm new to this forum, but I've been a stove bolt member for a few years now. I've been having some starting/ motor turning over issues, and I was wondering if you guys can help put together the issue at hand.

There are a lot of unfinished threads with no exact answer, but I have found consistent information on lawn mower and tractor forums( about the same engine right? ��)

The problem:

Motor will not turn over with plugs installed. Motor spins freely with plugs removed.

This is consistent with 12v jump and 6v power.
Belt removed


It's a 1954 Chevrolet 3600, with the 235.

Important information:
The truck is still 6v (new harness)
It has a 55 or later flywheel( 168 tooth )
It has a freshly rebuilt 6v starter with a 12v bendix and armature
New Optima Red Top 6v
4 Gauge Battery Cables


4/26
Adjusted Valves to mechanical specs of .006 intake, and .013 for exhaust

Upgraded to new grounds/ and starter wire 2/0 wire
Freshly ground frame contacts and used dielectric grease

Jumped the starter with 12v battery still won't turn over.


The previous owner "apparently" rebuilt, or at least resealed the motor.

Possible causes?

Thicker Gauge Battery Cables
Adjusting the Valves
Bad Starter
Bad Engine(stuck valves?/ bearings etc)

Lwt me know what you guys think!
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