I just purchased a 1927 bungalow style house. The roof has no trusses and has exposed rafter tails with 1x6's placed between as a block. There are no lower vents and wondered how to proceed to correct this. I thought of drilling holes for round vents but wanted to confirm this is the correct approach.
In theory that is a legitimate option. The usual problem though is there is insulation behind the blocking that would obstruct any air flow. Retrofitting the necessary baffles to allow air to get past gets to be a lot of work and makes the cold spots at the eave even colder.
It sounds like you may have adequate ventilation except for the lack of benefit from the stack effect by having high and low vents. This of course is a good thing to strive for, but I'm questioning if it's really worth it if the existing vents are ample. Even if not, adding additional ventilation where it's easier may be a reasonable compromise to the ideal high/low configuration.