Success!
To address Rick's concerns: the starter (IMI) does not break-down as your Tilton does so could not just activate the solenoid. I did however pull the pinion forward into engagement with slip-joint pliers and found my .045" paper clip fit comfortably. Also about 3/4 of the pinion tooth engaged the ring gear.
In the spirit of 'WTF', I hit the key and it was beautiful. No noise or bind and complete release when I let the key go. It does turn the motor more slowly than the OEM did but it's very steady and appears strong. Mine always went off on the first hit of the key anyway.
The starter only weighs 8 pounds and clears headers and block by miles.
Many thanks for all advice and Rick's help is greatly appreciated.
Now to get that Toploader lump back in...