Hubie I can't see anywhere you say what gear you have on the gearbox, the reason I ask is because with a 24 tooth on the engine ( which you have now changed) and the rest of the gears standard, I'm thinking it would be quite feat to kick it over.
Anyway some overall ratio choices assuming you have a 19 tooth on the gearbox
standard 21 engine, 43 clutch, 19 gearbox, 42 wheel = overall ratio 4.53
Yours 24, 43, 19, 42 = overall 3.96
Sidecar 21, 43, 18, 42 = overall 4.78 or 20, 43, 19, 42 = overall 4.75
Yours now 22, 43, 19, 42 = overall 4.32
mine to get just a tad more acceleration 22, 43, 18, 42 = 4.56
4.32 is still a good bit higher than standard ( 4.53 ) a difference of 0.21, consider that sidecar ratio is a difference of 0.22 or 0.25, so you are still as much higher than side car gearing is lower, also consider that added to all this is you gearbox ratios which help your engine in the lower gears but by the time you get to top the full effect of your overall ratio will become more pronounced
As per usual my maths are open to scrutiny
(another pet hate - why all of a sudden has it become MATH in place of MATHS)