Thanks to kirky's generous hint I've completed the puzzle. I'd made difficulties for myself by assuming that 'altered to fit' meant a change of length. This again emphasises the value ot this thread at a time when Mrs Seal and I are locked-down on a Norfolk sandbank.
Despite the hint I still can't parse 28 across. I have the answer because of the link with 40, but assume it isn't thematic. Any assistance would be appreciated.
Otherwise, once I'd understood the changes required, a very nice puzzle so my gratitude to the setter.