Thought I would chime in as I am roughly in your neighborhood in terms of times. A few years back I did 1:24 and then 2:57 and then more recently 1:28/3:07. So, assuming you train adequately, doubling your half time and adding about 10 minutes is about right in my view.
In terms of training, don't forget that you are an old man. Recovery matters a lot. Dropping weight and increasing miles will help, but I don't know too many 40+ runners who really could handle adding doubles, etc. I think you should increase what you are doing moderately, but keep a day off each week. Doubles is a high risk strategy you might want to take, but I think you are risking not getting to the starting line if you do that.