You can replace HR zones with a 2 mile/3km flat time trial... this will give you a base pace which corresponds fairly accurately with your max useable HR.
Then work out percentages from there. Its a decent guide but not infallible... for instance, the pace i run my rep sessions, i should be posting up better times at 5km and 10km... but its not quite as simple as that... is the answer that i'm pushing my rep sessions too hard...? or am i not pushing hard enough to reach my potential in flat races? Or am i missing something else like not enough "tempo" sessions? Or am i simply doing too much? Or does my constant fellracing schedule impinge on my flat performance? Who knows.....
Where i think pace/HR as a guide is very useful is for learning what your easy pace should be for the "80" of your training. ie 60-70% of max HR/3km pace.... for example my recent 3km race time suggests my easy running should be at 8:00-9:30/mile.... this is the tough part, because to run steadily even at the quicker end of that pace can feel incredibly slow at times.