As it becomes ever harder to source genuine Turbo engines, & near impossible to find one which doesn't need a total rebuild many people are now using a stock 1275 A+ unit as the basis for their engine, & why not ?
There's no reason a standard 1275 cannot be used as a basis for a Turbocharged engine, infact the idea is a sound one. These engines are usually in far better condition & are essentially the same, so with a few parts changed can become a good base for a suitable Turbo engine conversion.

With the youngest of the genuine Metro Turbo engines now 20 years old, the chances of finding one which doesn't need a rebuild are very rare. Most of these engines will have had a hard life and require a complete rebuild anyway. With people currently paying stupid prices for unproven Turbo engines on the likes of eBay a standard 1275 is a cheaper option. The main difference in the Turbo engine over its NA counterpart is in the pistons, the Turbo having a larger dished, Turbo specific, stronger item. As I said before, the chances of finding a standard Turbo engine which doesn't need a rebore are very rare, so you'll need new pistons anyway. So rebuilding the NA 1275 with suitable Turbo piston will basically give you a Metro Turbo engine & have cost you a lot less.
The bolt on parts such as the carb, Turbo etc can then be sourced and added.