Banding, (cutting the wheel down the middle & adding a hoop of fresh metal to widen it), used to be frowned on & deemed unsafe, but technology has come on a bit in recent years & it can be done far more accurately these days. Tanya had a set of Moggy Minor wheels banded by 4 inches for her trike project by a guy who does them for stock car racing. If they'll withstand the rigours of track use they're good enough for us. 40 quid a wheel if I remember right. Yes, the centre holes clear the Reliant hubs, but she's got disc brakes rather than drums. Because the banded wheels retain the original centres they still have the mounting lugs for hub caps, though she won't be using them.
Check back through her trike build thread in Trike Tech to see how they worked out.
Tazet's trike build