[TowerTalk] 40 meter beams

[Van Fair]

I am seriously considering replacing my old Mosley Pro 67A with a new SteppIR 4 element yagi and above or below it a 2 element 40 meter yagi. 
Due to tower limitations ( 16 sq ft) I need to use a small 40 meter beam and I am looking for positive and negative comments on all commercially available 2 element 40 meter yagi beams.  The tower height is 68 feet and is Rohn 25 G guyed at the top and the middle with 1/4 Phillystrand. Your comments will be appreciated.

 I also have a problem about the spacing between the SteppIR and the 2 element 40.  I believe I am limited by tower considerations to about 6 feet of separation and I am concerned about interaction especially on 15 meters. Any one have any experience in this area. I dont model but has anyone modeled a 2 element 40 over or under a 4 element 15 meter monibander on a 32 foot boom as the SteppIR is configured. Anyone good at modeling willing to do  a study?

This is a great group and I have learned a lot.  With 50 years in ham radio there is more to learn each day.  Thanks Van W4GIW