So...in 2023 do people still build hyd flat tappet engines * no rollers

I just slid in a thumper into a 360 for a ‘91 4 X 4 W150.
Zero issues.

I take apart every lifter and clean them up and out for a double check.
The other important item I don’t see written about and wonder if it is done is to make sure the lifter bore is clear and clean as much as possible. As well as drop the lifter in, rotate the lifter around in its bore with a light oil & make sure it slides up and down beyond its normal travel range.

Then, after those checks, rotate the cam with the lifters on top of the cam to make sure the lifters rotate as well. If all of the above is done and checks out OK, the probability of failure is greatly reduced but not guaranteed. Just take the time to check & double check.