4-speed o/d swap

Your existing 318 - 3spd flywheel is the correct one to use with the 318 OD 4spd bellhousing so you do not need to purchase one. Both use the 130 tooth flywheel. Nearly all slant 6's used a 122 (not 124) tooth flywheel creating the need for a different flywheel when doing a conversion from a 6 to and 8 or vice versa. They only thing that may (I say may cause I'm not absolutely 100% sure) need fabbing is the "Z" bar (or pedal cross shaft) mount at the bellhousing. The OD bell-housing may have a different pattern here depending on it's year of manufacture.