Mark, yr phrase "the evil curse of indecision" is spot on.
I'm usually pretty organised and like to map things out in my head before I even start a project and that's how it was until the Yamaha idea came up. The Hindall Yamaha and Cheney also got in the way so the little Rickman project started to get a little flaky. That indecision is now in the past, I'm going with the Maico.
I'll use the cutaway barrel, and the nice little 250 square bottom end that's got a Yamaha rod and big end, Motoplat ignition and some other little tricks. I hope to be able to use an up pipe, when I had the 360 RT1 engine in there for a dummy build the the Torque Industries DT2MX pipe fitted really well. I'll either modifiy it to suit the Maico or get GMC or Lozza to make me one. I'm still undecided (
theres that word again) on whether I'll use oval outer clutch cover or sand cast later model case, I'll wait until I get it in there properly first. The problem with the case being in behind the swingarm pivot isn't as dramatic as it appears in the photo, the engine is a little crooked in that shot. The bare frame photo shows the engine exactly where it should be and it's not so bad. It'll be pretty easy to get sprocket alignment.
I've got to disagree with you on the square tail section. The very reason I changed over to my smicko Mk3 glass is that I hate the Mk 4 boxy look. The Maico swingarm is so perfect. It's 95% bolt up, the only things that'll need changing are the torque arm and shock mounting points. I had a bit of a fiddle with the Metisse today and I must admit that I'm a bit excited about getting back into it. As soon as the Hindalls are finished I'll make a start on it.