I know this is old but thought I'd add another opiton seeing as Stu recently linked to this over on another forum.
This is the easiest way to bleed the system:
I designed this a number of years ago and have installed one on every engine since. The M-25 has a spot for a real ball valve on top of the t-stat housing.
1- Fill the engine as much as you can with antifreeze via the manifold.
2- Do yourself a favor and lose the sub par, burn your fingers, twist and open "pet cock" and replace it with a real ball valve. This one is male X female to reduce the number of fittings. Then connect a hose barb and a three to four foot piece of clear PVC hose. This hose now becomes your engines new "high spot" for both venting and purging air AND topping up with antifreeze..
3- Open the pet cock/ball valve and fire up the engine with the hose held high above it and let her run.
4- As the engine warms and the t-stat opens fluid may rise in the hose. As it drops, when the stat opens, use a transmission fluid funnel connected to the hose to fill it with antifreeze. Eventually the fluid will never dip back into the t-stat cap as the t-stat opens and closes. At that point the system is full and all the air has been purged.
5- Close the valve.
6- To drain any remaining antifreeze in the hose simply dip the hose end into an empty soda bottle to capture what is stuck in the hose after you closed the valve and you're good to go. Air and antifreeze DON'T mix well, especially if you are using Death Cool (AKA DexCool)...;)