Re: Old-style MC2100 automatic choke question
If you drill into the ex manfold and run it to the carb you'll have EGR - not desirable.
Notice the small holes you've seen on exhaust manifolds do not go into the exhaust stream. There's a big blind cavity in the manifold - called a choke stove - it heats air, then the carb sucks a little up into the carb for heating the choke coil.
You can make your own choke stove - simply wrap a length of tube around the exhaust manifold or even the exhaust pipe underneath where it won't show - and will gather heat. Leave one end slightly open - a tiny hole, hook the other end to the carb. You need a slight draft to get the hot air to flow - that's why the tiny hole.