First of all, do an extensive search on Roush engine problems on this forum and then choose wisely. Read their warranty closely. Does not cover
oil usage and getting service means you must pull the engine and ship to them. Find a local engine builder if you can.
If you do go with the 427SR, and IF you have roads where you can safely cruise at 70-75 mph, then the stock 3.46 rear end and the .64 fifth gear will be fine. The SR engine is a torquer and will cruise effortlessly at 2000 rpm and still pull away quickly if more pedal is added. If you are limited to speeds of less than 65-70, then get the .82 fifth gear with the stock rear end.
Since you are so far away, if you want to set the car up properly from the start, have the cobra valley ball joints, adjustable shocks and 450 lb springs, along with their front and rear sway bars installed. They vastly improve the handling and overall feel of the car.
If you look at my specs, I have the same setup you are thinking of, and the engine has been nothing but a headache for me and several others. Mine needed a complete rebuild after 13,000 miles with no help from Roush. If you are set on the name Roush, buy a different engine and I will send you my Roush valve covers and air cleaner. After the rebuild, I replaced anything that had their name on it.
Once again, just my opinion. Enjoy the ride.