Continued with the engine cowl today, struggling to get the two halves to get even remotely close to mating together. The instructions for this stage are remarkably lacking in detail, to the point you're left to guess how to proceed.
Anyway, I cut away a portion of the bottom cowl (hatched area in first picture below), then took to the inside surface of the top cowl with a die grinder. After much work I eventually got the two pieces to marry up together. Not pretty, but good enough for now. Apparently some fibreglass work later will fix all evils.
Guessing that I need to trim away a decent part of the air dam wall to get the two pieces together
Grinding away the inner surface of the top cowl, so the bottom half has any chance of fitting inside