I've done just that on my recently built 360.
Some of the crap hydraulic lifters were collapsing, a couple during idling, some collapsed during some sustained higher rpm revving.
Got sick and tired of it (same happened year ago on a bigblock built) and made spacers from simple tubing with I put under the internal piston in the lifter.
'Soft' iron tubing means the material will compress some during operation, so prepared to adjust the valves about every week for the first month orso. Proper metal would be stainless steel which is tougher and will resist the light hammering of the valve lash better.
