Hello.Welcome.
On the 68 model mustangs the front spindles were the same for the drum brake/disc brake cars. The only cars that got 9 inch rear ends in the 65-68 model years, any of which would work for your car,were 390/428 cars and the K codes,making the cost of just buying a parts car pretty ridiculous.It isn't complicated to go to a 4-speed, but it isn't really cheap either.A top loader is going to set you back better than a grand.Then you still need a shifter and linkage,bell housing, flywheel, clutch, clutch linkage, fork, clutch and brake pedals, and starter.A 9 inch rear end isn't going to be cheap either.If you can find one locally, so that the shipping doesn't kill you, that you don't have to relocate the spring perches and shorten the axle housing tubes,that also will set you back better than a grand.An 8 inch would be a little cheaper, but not much.But, if your car still has that silly integral carrier (6cyl rear end) it will actually be cheaper in the long run to swap it out with an 8 or 9 inch.Hope that helps and again,welcome.
On the 68 model mustangs the front spindles were the same for the drum brake/disc brake cars. The only cars that got 9 inch rear ends in the 65-68 model years, any of which would work for your car,were 390/428 cars and the K codes,making the cost of just buying a parts car pretty ridiculous.It isn't complicated to go to a 4-speed, but it isn't really cheap either.A top loader is going to set you back better than a grand.Then you still need a shifter and linkage,bell housing, flywheel, clutch, clutch linkage, fork, clutch and brake pedals, and starter.A 9 inch rear end isn't going to be cheap either.If you can find one locally, so that the shipping doesn't kill you, that you don't have to relocate the spring perches and shorten the axle housing tubes,that also will set you back better than a grand.An 8 inch would be a little cheaper, but not much.But, if your car still has that silly integral carrier (6cyl rear end) it will actually be cheaper in the long run to swap it out with an 8 or 9 inch.Hope that helps and again,welcome.
