Hi,
Well, if it's only two products, it's quite easy:
- in product A set a weight of 9999Kg
- in product B set a weight of 0.001Kg
- create a shipping method for the manual shipping plugin with a minnimum weight of 9999Kg and a price of £0
- create a shipping method for the manual shipping plugin with a maximum weight of 9998 Kg, a price of £4 and the name "3-5 day"
- create a shipping method for the manual shipping plugin with a maximum weight of 9998 Kg, a price of £6.5 and the name "next day"
Now, with more products / rules, it might get impractical...