Without seeing the full revised award I’d vote for the capital option for the payments of 1/7/03 (£4.18 & £134.51) as the regular instalment day continues on a Friday.
As the payments are paid weekly I would treat the change of circumstances as occuring on 4/7/03 the date of the first revised award, as per 1308 of the Tax Credit handbook. (1503 appears to contradict this but I think that it is relating to 4 weekly payments)
To calculate the new weekly income :-
1) Work out how much is still to be paid. I.E. the amount of the revised annual award less (total of instalments paid up to and including 27/6 and the payments of 1/7/03)
2) divide by the number of days between 4/7/03 and 5/4/04 (i.e. 277 days) and multiply by 7
…….or toss a coin – probably a more reliable method !