Thats good to hear Geeman, about the progress, you've done well there. Sure speedo will be fine just make sure it reads slightly higher than a satnav and you'll be fine, as long as you are using the same circumference tyres as the sierra you'll be fine.
CVH engines are available, there are 2 on e-bay. The one below comes with box and you'll get your money back selling that on its own:
http://www.ebay.co.uk/itm/FORD-SIERR...item1e66a7dd2a
Well Done........AndyH