Hi Kyle, as Shayne above, only I don't have a clue about the UK suppliers of SAS zorsts, either!
BTW Shayne the steering wheel on an 80 is just in front of the driver, except when my mrs is in the back, then she lets me steer
Back to ss zorsts, you won't regret it, but I do advise going for a good one. As with all zorsts, one that doesn't fit is just a PITA from day one onwards.
The guy that made mine went to a lot of trouble explaining that without a turbo a 3" would actually be slightly detrimental because I needed some back pressure on a naturally aspirated engine. You do have a turbo, so subject to the dia of the turbo outlet, you may get benefit from a 3".
In any event, don't just buy the cheapest, you'll have it for the remaining lifetime of the truck, so go for a good one. You won't regret it, that's a fact IMO.