Tripdog had done a simlar mod some time ago on a 6538 he custom machined his shim and pressed it into the case. Yours is like a dial spacer between the dial and movement?If you want to put a smaller dial in a larger case you could always use a shim....these come in various sizes, and are thin enough though cut with scissors...
Here is an example of one used before I sourced a Viet rep case for is 369 sub(just to keep it Explorer relevant).
Check out 0.1mm Shim Washers DIN 988 High Quality Steel - Multiple Sizes Available on eBay!
https://www.ebay.co.uk/itm/22439636...r=523181535899&widget_ver=artemis&media=EMAIL