Keep an eye out in the scrappies and call Ford scrap specialists. You will find a crack-free original dash eventually. I found one, and I wish I had taken it out to sell, but I couldn't be asked at the time. While Mk1 Sierras are very hard to come by now, Ford used parts specialists will stock them. (I know a place in Leeds that will deffo have one).

The later dashes (less speakerhole) are much more resistant to cracking than the early ones, not to mention easier to find. I changed mine to the later-style and never looked back. Just keep in mind you will require the inner A-beam trim from the Mk2 Sierra as well, and will need redrilling a different mounting hole in the A-beam.