What retainers to use?

Look up what retainers are recommended for the comp springs, check the inner/outer diameters of the 901’s and your Enginetechs and source retainers that cross-reference of your looking for all options. You have to do some sleuthing at the minimum if you don’t have a dial caliper to check everything yourself. Definitely don’t use the oem stock retainers, they are too loose a fit for those springs.