FWIW.. it is very common for the retainer OD to be smaller that the spring OD. This Comp retainer sizing chart list a 1.400" OD retainer for 3/8" valve stem Mopar springs with OD's from 1.437 to 1.500". So it depends on the 'x' in 1.3x" if they are suitable.
https://static.speedwaymotors.com/images/PDF/COMP-Retainers-Sizing-Chart.pdf
