If you are putting the 250 motor into a 1955 Chev car, you can use the stock '55 V-8 bellhousing and bolt it to the 250 motor. This will give you a good starting point as you will have the back of the motor aligned and all your original clutch linkage will work. Just install the T-5 onto the V-8 housing and then make up your side mounts wherever they line up on the chassis.
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Ontario Inliners
1940 Chev Sedan
1954 Chev Custom
1965 Chev Pick-up