With a standard hydraulic setup the lifter pre-load is set by the pushrod length and isn't ajustable unless you change the pushrod length or fit adjustable rockers. In your case, as long as you fit direct replacement standard lifters you don't need to do either as long as the heads/block haven't been re-surfaced by a great amount. Out of interest, are you absolutely sure the heads have never been off? Re-surfacing the heads and/or block acts to reduce the installed height of the rocker arm (the distance between the cam lobe and the installed rocker arm - if you follow what I mean), which can lead to geometry issues (very rare but possible) with the pushrods now needing to be shorter than standard.
What was the make and part number (on the paperwork) for your lifters? By racing lifters I guess they are saying "anti pump-up" lifters which (as you mention) tend to bleed down quicker - the possible cause of your "easy to compress" issue you raised.
Leaving them in oil overnight should be plenty unless you were using very thick oil (SAE60 or greater), the thinner the oil the better to fill them with and don't forget to moly the lobe mating surface well. You can "pump them" if you want to but that oil will be exhausted out of the lifter anyway when you install them.
Just fit the new standard replacement lifters, pushrods and rockers and torque them up. The only thing to remember is to torque the rockers with the valves in the closed position and when you start the engine make sure you run-in the cam and lifters exactly as described on you cam spec sheet, then turn the engine off and change the oil and filter while it is still hot.
I have to ask, have you addressed the cause of the oiling issue that caused the cam to chew a lobe in the first place?
Regards,
Dave.
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