It is a 445 running about 10 to 1 compression in a '69 F100 4WD. I'm running Sanderson Shorty Headers, so I don't think I have an fitment problem. Was running a stock Starter for the past 18 years, and who knows before that because this is the starter that came on the old 360.
Tried to start it yesterday and I forgot to open the fuel cut off, so cranked it for 5 seconds, stopped, tried again and the starter stayed engaged. Pulled the ground off the battery to stop it. A friend and old Ford hand said he had seen that occasionally when the battery was low (mine was at around 12.3 v, but it would normally start at that level), so I charged it and when I put the ground back on it started trying to crank but it made a loud bang.
I'll pull it today, but it is time for a new starter.