i am hopefully fitting my exhaust this weekend after sitting in the dinning room for the last few months.

my main issue is the centre pipe to downpipe connection.
The centre has a floating flange which bolts through to the downpipe with two long bolts with springs.
The end of the pipe is blown out like a trumpet.
i was hoping to use the gasket on the car already but it doesn't look in good shape.

The downpipe size is 3" (inside)
The centre pipe is 3" that narrows at the end to 2.5" with a 3" trumpet.

do i need this 2.5" cone gasket http://www.ebay.co.uk/itm/GENUINE-SU...4#ht_515wt_936

or do i need a 3" to 3"?

car is a '00' classic if that makes any difference
hopefully this makes sense