300 SDL custom exhaust project

[OhioSDL]

My 87 300 sdl badly needed some new plumbing to get all that smoke rear of the passenger cabin so I decided to "save" some money and try doing this on my own. What I have now is the factory exhaust from the turbo to the cat. everything rear needs replaced. Ive ordered the following. 1 flowmaster series 50 muffler (flowmaster part #842551) and the flowmaster universal talpipe kit (15901) which includes 12 ft of mandrel bent tubing to custom route.

My questions are this:
1. Should I mount the one muffler in the center in place of the resinator or in the rear muffler well. This muffler fits well in both locations.
2. The cat. I need to find a transition from the 3 bolt flange to my 2.5 in system. I belive that the flange attached to the back of the cat is 2.25 in? does anyone know of such a beast or should I wack off the whole thing and limit my much improved driving to off road only?

And to answer the commonly asked questions:

yes the recall for the ox trap has been completed just reciently and no the dealer didnt replace the turbo Im going to tackle that also even though it only uses 1 qt of oil in 2000 mi.

no the head hasnt given out on me.... yet.

no I dont plan on building a fire-breathing propane 24 lb boost tire eating machine, just looking for ways to have fun, get dirty and not lay out too much cash... even though it is mercedes.

many thanks for you imput.