If one replaces the stock HD lifter (ie HD# 18538-99C) with an aftermarket one (ie S&S Premium High Performance 330-0175 or High Performance 33-5350) can one still use their stock non-adjustable pushrods?

 

Yes, if all other things in there remain about the same height.
Nonadjustable are just a PIA .

 

yes as long as you are using the stoc cam or a cam that has the same base circle spec as a stock cam, you can use the stock pushrods. just as a note, a lot of people go to adjustable pushrods so that they can do cam/lifter/oil pump stuff without the need to take apart the rocker boxes.
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