OldIHC

1969 International M800 POSTOFFICE Van, Engine 3.8L 232cid L6:

I understand the base timing is supposed to be 3 degrees BTC on this engine. Could someone give me a detailed explanation of what "base timing" means and exactly how to set the timing?

Thanks.

232 would be the AMC six that IHC bought and installed. Base timing means vac-advance dis connected and plugged and engine turning slow enough that the mechanical advance as not started to advance the timing, in other words slow idle of around 500 to 600 RPM.
I don't remember where AMC placed the timing marks but look around the front pulley/damper.

Could also look to the AMC forums for the 232 motor

To do it right you have to check that mechanical and vacuum advances are working. They are often both inop.
Do this: with vacuum advance plugged off install a timing light and rev engine a bit. Timing should always go back to the same place and mechanical advance should be all in by 2000 RPM or so. Expect 15-17 degrees added by mechanical advance. With engine off remove distributor cap, grab rotor, twist in direction of rotation and release. It should snap back. A rotor that is lazy to return means that mechanical advance is sketchy at best. It needs to be lubricated and exercised until it's free again. VERY common to see stuck mechanical advance. NO movement of rotor at all.
With cap back on start engine and apply vacuum to vacuum advance. Again you should see 15ish degrees added (this time at idle). If not, vacuum advance is inop. Very common.
Ignition advance is to make up for amount of time that combustion takes at any load or engine speed.
Base timing (where dist. is set) plus mechanical advance plus vacuum advance equals total advance.
An old Motors Manual has all these specs in the distributor section.
Setting a vehicle's ignition base timing ASSUMES that mechanical and vacuum advances are working. MANY a distributor has been mistakenly clocked in the over-advanced position to make up for poor engine performance. Everyone seems to blame ignition timing for all performance woes. Check to see if all your advances are working.
Point dwell or point gap is directly related to timing.