Rebuild the Zenith. If anything, it may be a tad large, not small. Would easily support a larger cam, head work, and improved exhaust if you have the desire to ever make these changes.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop