On the subeject of the flywheel, the 230 and 218 flywheels don't interchange anyway. The 218 is 4-bolt (with dowelling around the bolts, IIRC) and the 230 is 8-bolt.
But for roundy-roundy cars I wouldn't have thought flywheel weight was important. At least for performance, maybe for reliability, and maybe for harmonics.
Think about gearing too... is there any advantage to running an overdrive?
Personally, I don't think deck thickness is an issue at all. These were pretty heavy blocks.
