Pilot shaft on a 4cyl t-5 is 7 1/8" vs the V8 6 5/8" also, not just the diameter difference.
The SVO t5 also has a steeeep first gear, 4.something versus the v8 2.95 or 3.35. Can be nice in a car with a 2.73/3.08 rear gear, but I'm pretty sure it'll make first gear useless with numerically higher rear gears.
I happen to have a 85 SVO t5....and it will hold up behind a v8, but I don't recommend it, I noticed some interference marks on the pilot shaft and bearing after I replaced it with a FMS z tranny I lucked into out of a 92.