I ran into the same problem as you when I did my tranny swap -- couldn't source an 8-bolt flywheel.

I took my 6-bolt flywheel to carolinaclutch.com and spoke with the owner there about what I could do. His company specializes in making custom high-performance flywheel/clutch combos (we're talking racing applications for 1000+ hp vettes and crap). He said that machining the correct bolt pattern into the flywheel would be just fine, and welding in the leftover holes would simply be overkill.

I mentioned that others had thought the flywheel would disintegrate and chop off my legs. He said that yes, it would . . . if I were pushing somewhere close to about 800 hp at roughly 8000 to 10000 rpm. In other words, no way, no how for a stock, or even highly modified, B30.

That said, my flywheel was in very good condition, so your mileage may vary. While the risk of catastrophic failure exists . . . I think the probability is extremely low.

On another note . . . weren't you parting out a 164? I'm in need of a known-to-be-good water pump. Got one available?
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74 164E