After about 4 years of development I have finalised the design!!
The early MGF had a 4 stud manifold WCD106001  (currently not available} and was changed around Sept 1999 at chassis number YD522572 to the 6 stud manifold WCD106091. Check which manifold you have before ordering. Note 4stud item can take a week or so if not in stock!
Order 6 stud gasket if required .see list of parts below.
The stock down pipe has a flexible mid section that can fail prematurely. In addition the stock part is made with several compromises. The bends are poor with kinking/necking thus reducing bore diameter, which is not good for efficient gas flow. The two into one collector causes a restriction due to loss of cross sectional area and the lambda sensor port is often restricted due to poor manufacturing techniques/mass production methods.
The oval section flexi section also flattens the inlet pipe thus causing a restriction! Aftermarket ones are even worse with proven power losses and changes the sound of the exhaust!! The two pipes are usually have a reduced cross section where the two flow into one. This often makes the car sound raspy like a VW Beetle!! 
My new design uses mandrel bent stainless steel tube and good component design. The improvements are better flow rates and performance.
The troublesome flexy section has been replaced with the same section we use on the 4.2.1 manifold making it an easy job to replace the flexy section but also can be upgraded with the 421 at a later date thus saving money and gaining power and torque!
The design takes the two pipes from the manifold under the sump before converging into  the Y piece collector. This design increases both torque and BHP . Without loss of ground clearance.
Comes with the usual MS and Piper cast iron warranty so you can buy with confidence!! Note some companies are charging over £300 -£350 for a copy of the stock item!!
Feedback from recent customers show a positive power and torque increase over the stock part! See review.
Note replaces4 stud manifold part No WCD106001 and 6 stud manifold WCD106091