Keep it as simple as possible....call it Classic Upright Slider class and make it eligible to all upright engined sliders with no leading link front ends. Simple enough for even the dumbest of the dumb to understand. Keep the 2v class as a pre 75 only class, no centre port frames and leading link front ends, basically as it's always been. If you start trying to work out year specific cutoff eras you'll open a can of worms (not pun intended Trev). There'll always be engines that will be deemed as uncompetitive but that's far better than continuous argument over when the first GM came out or whether an 892 Jawa should be in the same class as an 895. All Goddens, Weslakes, Jawas, GM's and 4V conversions on 2V Jawas all in the same mixing pot.