[Jac Mac]

Hmmm, interesting method of checking cruise HC. If it was mine & I had to comply with your regs I would employ all of the following to improve the carb signal etc.
1. Anti Reversion cones in headers.
2. Anti Reversion plates under each carb.
3. Mod the carbs for Non PV operation.
4. Recurve dizzy advance and use a manifold vac advance source along with electric vac switch which is only activated by microswitch to trans shifter when in neutral/first/reverse.
5. Use electric solenoid to set running idle speed so that when you kill ignition it goes back to a minimal idle speed which will prevent run/on.
6. Fit vac pump to lower crankcase pressure ( Preferably dry sump setup, but anything will help )