I'm building one now, albeit slowly, and yes , the instructions are vague in some areas. The good news is that Lynn will clarify matters over the phone or by e-mail. I've built a gazillion models since the early sixties - from a Berkeley Bulpup to a 35% Carden and I must admit that the instructions have me scratching my head at times, despite having the plans and measuring. I'm using a OS55ax and 10 ounce Dubro tank. Good Luck !