This is very similar to how I trained back in 1982....and ended up running 2:23 in The New York Marathon..... Based on what you wrote it seems like you can run faster than 2:27.
Like you, I chose to close hard, like sub-16:00 for the last 5K on a couple of the mid-longer runs--- but it was more palatable o do that on 12-15 milers as opposed to the 23 milers. Had a lot of sub-58:00 10 milers closing in 10:30 last 2M. I would throw in workouts like 4 X 400 in 0:58 with 400M jog in between, then a nice distance run after (I have no raw speed). I did a lot of it on my own so don't think you can't train alone when necessary.
I also ran a 25K race three weeks out which definitely helped a lot. Actually, I ran the 25K at a 5:39 pace then the Marathon three weeks later at a 5:28 pace into a North East Wind. The 25K did wonders.
Unless sponsored by Nike or somebody, you can get a near-max benefit from self training, mixing in a combination of hard closes, occasional long runs, doing repeats of your good choice, racing/not over racing and maintaining a good base to achieve / get you 90 percent to where you want to go.
It worked for me.....
Good Luck.