That sounds good! Very close to what I'm doing right now, although it seems you were in better shape in April than I was, so maybe you're farther along now than you think! :)
*All of these paces are based on my GPS watch, which would be about 5 secs/mile slower than actual pace in a race due to tangents or whatever
8/13: First 13 of 26.2 @7:15 (HR 163) - Ran a 3:21 (HR 166 avg/180 pk)
8/14: First 13 of 26.2 @7:18 (HR 157) - Ran a 3:15 (HR 163 avg/181 pk)
11/14: First 13 of 26.2 @7:15 (HR 151) - Ran a 3:10 (current PR) (HR 153avg /174 pk)
4/16: First 13 miles of 26.2 @7:05 (HR 162) - Ran a 3:11:17 (injured during training but tried for PR anyway - nothin' to lose!) (HR 162 avg/171 pk)
As you can see from the data above, my best race had the lowest average and peak heart rate.
Recent heart rates (once again, paces by GPS):
HM: First 13 of 13.1 @6:23 (HR 157) - Ran a 1:24:21
T (4x2 middle of 18 mile run) @6:22 (HR 158)
M (12 cont. miles middle of 17 miles): @6:45 (HR 158)
E (20 cont. miles): @7:30 (HR 136)
The recent paces above were run in shirt-off-hotter-than-comfortable weather except for the HM. Otherwise, I think that HR would be higher!
I'm trying to be careful! I definitely feel beat up, but I'm hoping for some relief tomorrow because I have one more 20 miler scheduled. Yes, I've been running 16-18 miles 2 times a week with workouts just like you're describing in the middle. It's definitely helping me out! I used to be a big fan of the 20 mile progressive run, but if these workouts within a long run workout work out for my upcoming race, than I just might be a Jack Daniels convert!
Good luck to you, too!