Kyphur your T-56 six speed trans allows the use of a much larger cam, but 1scryd has a three speed auto. The T-56 also allows one to go slightly higher on the comp. range, as you have a multitude of gears to keep the load off the engine. I think your wanting the 4.56 is bit low. It certainly will keep your gears close, but if you have a 400 engine, they have decent torque range. If your on the street then you may concider a 4.11 I did a lot of gear changing on my Dodge Vipers over the years, and they come with the T-56 trans, and found the 3.55's to be great, but the 500 hp V-10 Viper engine had liberal amounts of low end torque. Actually your car may do well with no more than a 4.11 gear for street and strip.
ps, yes I'm Skip White from Skip White Performance in Kingsport TN