i tried to modify the face of CJ in san andreas to make a skin of Michael, but the cj face has so tipical curves od a black man, because of waht th emichael face gets deformed. 
 
I think there will be so difficult to make a michael skin for SA. We will have to wait till someone will model a new player model for SA. 
About the wheel size, have to modify the parameters of the car in the file vehicles.ide, replace(try) with this:( i use infernus for kitt):
411, 	infernus, 	infernus, 	car, 		infernus,	infernus, 	null,	executive, 	5, 	0,	0,		1, 0.9, 0.9,		0
By the other hand, i can tell you that perhaps we can make a kitt model for SA with MOVING SCANNER.We have to try it still, but we know how to do it(3dstudio max).
Too we are making the first demos of the semi:(still not ended)
