That's an awful longggggg tranny.
The T5 from bolt up (excluding bellhousing is just short of 500mm)
The tremec 3550 series including the new TK500/600 is exactly the same.ie 19.75"approx.
The toploader is an excellent tranny but come in several flavours. You might want to go to the transmission forum in here and have a read.
http://www.clubcobra.com/forums/foru...?s=&forumid=92
Also go have a look at David Kees site to identify which top loader you are looking at.
http://www.4speedtoploaders.com/
The tremecs are assentially a 5 speed top loader. The newer version TR500/600 have much better ratios than the earlier 3550 and TKS versions, and are capable of handling greater torque. (500 & 600 Ft/Lbs)
The WC T5 is good for about 300F/Lbs torque with the heavy duty z versions much more capable of handling higher torque.
If you want to stick with the T5 you have(if it is a T5) then you can get heavy duty internals from G-force in the states.
http://www.g-forcetransmissions.com/tran_gt-5.asp
However, If you were to go to that expense you may as well consider the new Tremec 500/600 for the better ratios.
But....I'm not sure what you have is a T5.
Cheers