Yeah, I'd say 4.30s are probably too low for your mods. If you didn't have as much power as you do, then they might be all right.
With a C4 you would probably be ok. The only thing you'd have to worry about is taching out before the finish line. Remember C4s don't have an OD like AODs do. Just 3 drive gears.
I do think that 4.30s are too steep for your set up right now. And someone else will have to tell you what to do about the C4.
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Previously "BennyBoy"
'69 Coupe with 351W-I rolled it 8/8
Edelbrock RPM intake, Edelbrock RPM cam, Edelbrock 750 cfm carb, Hedman headers, 2 1/2" pipe, glasspacks, C4: shift kit, 9" Currie: Trac-Lok 3.70s, 290hp-stock heads