Technical Vintage Mallory distributor HELP please...

Oddball IH stuff here. Hopefully someone can tell me a little bit about it. Model YGCH. If I decode it correctly:
Y= centrifugal advance
G= governor attachment
C= points type
H= ???

Found it in the catalog:


Original Delco distributor has external vacuum advance (distributor body rotates in block) like early Stovebolts. Do these old Mallory distributors eliminate external advance and have their own internal advance built in? It appears there is a port here:


Also... is this a candidate for a Pertronix conversion, specifically ML-161?

 

Jim @GMC BUBBA is back on here now so perhaps he can offer some guidance.

 

Can’t you take the cap off and while holding the drive gear at the base, try and twist the cam lobe, if it twists slightly back and forth it will have mechanical advance?

 

This is all I've seen that mentions the YGC-H specifically. Looks like possibly the -H might mean 'Heavy Duty', as all of the -H stuff is called out as using the HD breaker points.

 

Damn, you've sure got the paperwork! The lobe 'swing' is the mech. advance. Sometimes the bushings were worn...
Good capacitor?
Good point setting?
Twist near 6° initial
and fire here up.

 

Thanks Carter! Good info for us Mallory aficionados.

 

Man, you ain't kiddn'!!
@ CARTER -Thanks!!
I don't have this thing in hand. All I know is it came off of a running motor and is available for purchase...which is promising.
According to these part numbers, it seems all of these Mallory 6 cylinder distributors take the same caps, rotors, and condensers, and the same Echlin replacement parts, across the board. I *think* the Pertronix upgrade ML-161 will work as well then. It appears I will still have to use the external vacuum set up.

Maybe the port is for spark control?? What is the purpose in this case?? Found this, but still not sure what it does or if I'm even barking up the right tree:


I have reached out to GMC BUBBA and hope he has some insight.

 

Bubba knows, and does help many here. Let's hit him up.

 

If it's IH it may be for a governor

 

Give the man a cigar!!
Totally what it is. Found this on an ag site where the owner of a grain truck had similar questions about whether or not the distributor was centrifugal or vacuum advanced. Circled components were confirmed to be governor related: