I use the basic Goodwrench 350 with Edelbrock intake & Q-jet 4brl. Stock ramhorn ex. manifolds with duals. I don't drive them hard but I do put my foot in it once in a while. I wouldn't recommend the T-5 for heavy duty service but the Mustang guys don't baby them.
To change to the mech. speedo you have to get the speedo gears & the rear housing from the earliar mech. drive model. If you find one of those you might as well use it. They are getting hard to find lately.