Thanks guys, I really appreciate the advice.
To recap - I already have the rebuild kit with all bearings and syncros, a new steel bearing retainer (V8) plus a 4-cyl tranny that is in "nice" condition to use for the build. As such, it is economically feasible.
Q1: Can someone confirm to me that the main long shaft itself is the same between the 4-cyl and the 8-cyl T5? I am assuming yes, so that I can re-use my 4-cyl shaft with the new gearset and T5 rebuild kit (V8).
Yes, the main shaft is the same between a 4-cyl and a V8 Mustang T5.
Q2: I would indeed like a lower RPM fifth gear. The recommendation is to install a 2.95 gear set, however retain the gears for fifth? Those are the ones in the extension housing, correct?
Yes, the fifth gear pair is in the extension housing. As I was saying in the earlier post. The 4-cyl should have a 27/59 pair will yield a 0.59 ratio for fifth which will chug along economically on the highway. A racing fifth gear pair is available that will give a peppy 0.80 fifth gear. Re-read what I said above about available ratios.
Q3: Given what I have, I am thinking all I need is the complete 2.95 gearset, correct? (includes input shaft, gear shaft, and the gears).
Input, counter gear, first gear, second gear, third gear.
They are available in the top-quality OEM in Tremec-brand boxes, or in generic white, blue, or plain brown boxes that were made overseas and will work, but may not be as good.
You will need to choose the input shaft that is NOT for the T5Z so that it will match your output shaft. You need the 24t one with the part number that ends in "020."
The T5Z one ends in "060." Yours will have the 15 loose roller bearings and the T5Z uses a caged, tapered bearing set.
To reconfirm for you, all you need to convert a 4-cyl T5 to a Fox v8 type is the gears, the rebuild kit and the front retainer.