I'm Running the Colfax Marathon

I have decided to run the Colfax Marathon, May 18 in Denver rather than the Colorado Marathon, May 4 in Ft Collins. Denver is a lot closer than Ft Collins, the Colfax is an out-and-back meaning there is no 4 am bus ride to the start and I'll get another two weeks of training in. The Colfax was previously a one-way with the last 13 miles rising 400 ft in elevation. Last year the port-a-potties didn't show up and some underling reset the course in City Park so it was 27.5 miles. This year's course looks really good on paper. The start and finish are both located in City Park where there is adequate parking. The marathon heads West on Colfax Ave while the half marathon heads East and I will not be tempted to keep up with the faster half marathoners. The first three miles are flat, in mile 4 there is a drop of 100' down to the Platte River, there is a 400' gain from mile 4 to mile 10, miles 10-13 are flat, miles 13-21 drop 450', miles 21-23 gain 150', and mile 23 to the finish is flat. My plan is to run the first 13 miles at a heart rate of 137 bpm. I used this strategy several years ago in the Boulder Backroads marathon that also has an uphill first half and I felt strong at the finish. I will increase my heart rate to 140 bpm for miles 13-21 and 143 bpm to the finish. Typical strategies for running a marathon using target heart rates call for 3-4 beats increases at miles 13 and 20. I am delaying the increase to the low elevation on the course at about 21.3 miles.I really have no idea of what time I'll run. My 21:28 in the Kickoff Classic 5K last September predicts a 3:33 marathon according to the Bolder Boulder conversion charts. I ran a 3:54 in the 2005 Boulder Backroads marathon using this target heart rate strategy but that race is on gravel with much more elevation gains and loses. Actually, I don't care what my time is, I just want to not go out too fast and be strong at the finish.