Main jet tuning... ...in France

No, I don't think you should have bigger main jets.
I'm saying 64 and less is pretty small, and I'm wondering if your A/F gauge is giving you an erroneous reading. Where exactly have you installed it, and what brand is it?And at what rpm and throttle setting is it telling you that you are rich?

There are several fuel circuits in that carb, and each of them begins working at a different manifold vacuum level.
I assume you know that the required MJ is determined with the engine working as hard as it possibly can; as in WOT in third gear.
But, you can sometimes balance the MJ against the PV
A 383 with a 650, and a 223/[email protected] cam won't need much for fuel. But it probably idles with 16ish inches of vacuum at 750 rpm with 14* of timing. In which case a 6.5-PV is not the right one. By the book they say the PV should be 1/2 the idle vacuum. So for you, IF it idles at 16, then the PV should be16x1/2=8, And that would then be an 8.5, as the PVs are only available to the nearest .5 IIRC.
With the 8.5, the PV will start flowing earlier. Sometimes this allows a 1 or 2 MJ smaller for a streeter. Smaller from IDEAL, not smaller from your 68 or whatever. I like operating like this cuz most of the time you are on the low-speed circuit or the mains and only occasionally on the PV. So a little lean on the mains around town makes it snappy, and it doesn't want to pull in to every filling station.