I'll post the plans here and on the 1/2A all the way site when they're done.

I'd say somewhere around 22" for an .010 and 30" for an .020 should be good. As far as the reedies vs TeeDees goes, there is always a range of acceptable engines for any given design. I'd say that at the 40" span a Babe Bee would be the bottom end and a Norvel .071 would be the top.

Once the design itself is done, I already have a solution for scaling. However, that isn't my reason for drawing up this plan. I just thought it would be good to have a freely available plan for first time 1/2A flyers.