I'm sort of in the same boat.
A friend of mine who is my age, but not in shape (but no couch potato either) decided he needed to do something for himself and his family. He also is one of the more vocal one of my friends about what I do eventually really hurting me. Long story short he challenged me, and I accepted to train for an complete a triathlon sprint. In this case it is a 400 yd swim, 20 mile bike, and a 5k run.
The winner gets paid $500 with a $100 bonus if they beat the loser by 10 min or more.
Last year, when I was really training my anaerobic capacity I ran a 5k cold in 28:51. I have no idea about the swim or bike. The only thing there I have going for me, ia another frient, Jeff Tarkowski, is loaning me his bike. Jeff just turned pro as a triathlete. He is going to teach me to swim too.
The race is in June.
Jeff seems to think that I can train for this and not lose very much if any of my strength. I'm not sure I totally believe him, but he has a ton more experience with this than me, and at one time competed as a powerlifter. He also trained our other friend Jim Flannigan (Bears/Packers DT) to do half ironmans. Jim has come off his playing weight of 320 and is down to 255 and is a solid competitor in his age group, and still is strong as a bull. He does really no heavy strength work but still can squat 600, bench 405 and hang clean 315 (that bench and hang clean kill mine).
Jeff (trainer) believes that I should focus on keeping my protein at 1.5g/lb of bw, restrict my carbs to only complex as much as possible, and eat other foods with a very low glycemic content. Good fats are fine, and as long as I follow those rules, I can take in as many calories as I want. He feels that if I follow that, and train like he wants, along with my weight training, I should stay pretty close to my current strength levels, and if I do drop it wouldn't be more than 10%. If that's the case I should be able to get that 10% back pretty quick after the race. I will have the added benefit of having increased my VO2 max and lactic acid threshold levels.
I'm sorry I got so long winded, but I hope this helps.
B-