这是个并列复杂句,由and作为连接词.
先看and前面的那一句,“He had done a few days' navvy work when he could get it”是一个过去完成时态的时间状语从句（由于不知道句子的上下文,无从判断是否为假设句,若是假设句则为过去式）,这个句子的主干为“He had done a few days' navvy work ”,主语“He”,谓语“had done”（do的过去完成时）,宾语“a few days' navvy work ”其中navvy work为宾语的核心词,a few days'为前置定语,修饰navvy work；之前说过这是个时间状语从句,由when引导,从句的结构比较简单“主谓宾”结构没加任何修饰成分——“he could get it”
and后面为“he had run around the Domain in the early mornings to get his legs in shape”主干为“he had run ”——主谓结构,其他均为修饰成分."around the Domain"为地点状语,“in the early mornings”为时间状语,“to get his legs in shape”为目的状语,均修饰谓语“had run”,表明主语“he”跑步的时间,地点和锻炼目的.
此长句的翻译为“在他身体还可以的时候,他参加了几天海军.那个时候,他会每天绕着领地晨跑,来塑造腿型”