Basically, what Dan is getting at can be found here: http://www.ffh.us/cn/hadd.htm
More specifically, this page holds something interesting on what you are asking: http://www.ffh.us/cn/part3.htm
HRMs are optional of course. Basically, Hadd is rehashing Lydiard and other versions of rehashing Lydiard are done without HRMs. It just depends on who you end up reading.
Personally, for the last long run, I’d probably do most of the run at about 1:00/mile slower than marathon pace, then do up to the last 5 miles at a pace at or faster than marathon pace. However, the most important thing at this point is doing what you are comfortable with and what you have the most faith in.