well luckily i just investigated all into this and found that Laurel Mountain Mustang has a kit for doing this, comes with a cable clutch setup, a crossmember, all the sorts of parts for putting the tranny in your 65-73 mustang... the only thing it requires is that you get a tranny, a clutch pedal and use the flywheel and balancer off of a late model 5.0 mustang.... as long as you use both parts, it keeps the balance on the crank.... its reccomended to use the t5 from an 79-93 mustang because they had a shorter inputer shaft, which fits easier into a 66 mustang... so for a 5speed conversion it will cost me $75 for a tranny from the junkyard, $15 for the flywheel and balancer from the junkyard, $680 or so for the kit, and a possible $100 to have my drive shaft cut shorter since the t5 is longer than my c4.. not too bad really for putting a tranny in a car that never had the option of 5 gears