The stock pipe isn't 2.25", it's more like 1.75". I just cut the bit behind the cat off of a '93.
You have the DT header? IIRC it should have come with a connecting pipe which spans this section, to adapt w/ the new pipe size.

When i got my LCe header it came with this in the same package.
Not sure if the flanges are the same, but you might be able to get the connector from them if Thorley isn't making them anymore (??)

With 200+ Billion electrical parts, the world most complicated machine is inside your own skull.

Question Reality.
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'89 Rnr DLX "SR4.5", 32s w/ 5.29 locked f/r blah blah