Michael,
The T35 Mk1 had much deeper combustion chambers, so needed more advance. In practice, you will find that the T35 engines run sweetest with the ignition set just off full advance - this is more noticeable now that we are expected to run on unleaded petrol. I would suggest that you set the engine up to the original figures, then adjust the advance/retard lever to get the best performance, then mark that position on the lever with a small dab of paint. This may vary as the engine settles down - especially as the Douglas engine runs with tight wire advance, which makes the setting sensitive to cable stretch, etc. Always run with the ignition as far advanced as possible consistent with smooth running. Running retarded is likely to result in overheating - especially with unleaded fuel that tends to burn hotter than the old leaded petrol
Regards,
Eddie.