Personally I wouldn’t change the rules at all, nor would I play 41 instead.
It sounds counterintuitive, but the smaller games like 41 are frustrating because mistakes are compounded by lack of resources. You get much more leeway in battles in 40 than you do in 41.
I’d just jump in, let them play a power and maybe make suggestions if they ask, but let them make mistakes and no matter what, try to keep the insider talk between you and your friend to a minimum. In other words, don’t keep laying out stories or strategies, let them learn without making them feeling like they’re intruding or novices.
My wife plays a whole bunch of different games with us, but not any war stuff, except Risk.
Give them a primer of the game function, then just have a blast, no matter who wins. The only real way for them to enjoy or learn the game is to play and the only way to learn about bombers, cruisers, etc is to let it happen. They get bombed, they’ll see the worth. If they buy cruisers and they get destroyed, they’ll pick up on that better than if you say it.
Believe or not, a fresh set of brains in the mix might exploit something you’ve never seen. My son always pulls out some obscure move that kills a plan, whether he knows it or not.