Hi, I've put the ST170 engine and 6-speed gearbox in my Orion Mk1. I have been using a single belt to the alternator and use a Davis Craig EWP-80 electric water pump. The EWP is fine, but as it doesn't pump when the engine is cold soon on cold days no hot water gets into the heater matrix and in the winter it rather chilly.
So as I'm in the process of swapping the Getrag to the MTX 5-speed gearbox I'm also putting on individual throttle bodies (more on that later) and going back to the Ford water pump. So I'm making a couple of idler pulleys that simply bolt on allowing use of the stock Ford belt tensioner. All brackets are made of aerospace grade billet aluminium and the idler wheels are ribbed and brand new.
The Retro Ford kit and others like don't use a belt tensioner. The tensioner removes the headache of regular manual retensioning, multi rib belts don't stretch so work best when preloaded by tensioner.
I'm going to be selling my kit in a couple of weeks. If you're interested please get in touch, and if there's enough interest I will make a bulk order and pass on the discount.
The photo shows a mock up, but shows the stock serpentine belt path allowing for the correct water pump rotation and the ability to upgrade to air con and power steering unlike other auxiliary belt kits.
Cheers, Clive