I just went out to my storage. There is a 2.3l that I got in trade for some work. It has been built for salt lakes racing, so not stock...
However, I think it would be based on stock type engine. There is no hydraulic lifters. There are no lifters at all. There is a place to adjust the ball end of the rockers to provide clearances needed at the valve tip. Does yours look similar to this? If so you need to back off the adjusters because as the engine heats the clearances close up. And if too close to start with the valves will end up not closing onto the seats when warmed up. This is what it sounds like is happening....
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First pic, left side, under the spring is where the adjustment is made. To the right in between the valve stem and rocker is where the measurements for clearance would be taken with feeler gauges. Generally the intake would have less clearance than the exhaust.