Interesting. Those would be custom oversize valves.
The head has obviously been reworked. The only way to tell if the valve is damaged or not closed due to a broken spring is to disassemble it. Check the valve stem diameter, A B18 valve stem is larger than a B20 valve stem. A B18 Valve is a little longer than a B20 Valve. It may have been upgraded to a larger stem and guide also.
You say in your post that the lifters are not bent. Do you mean the rods are not bent?
The lifters are down below the top of the block, where the oil galley is, sitting in holes above the cam. From the cam lobes pounding and hi-rev's the bottom of the lifters get peaned and cannot be extracted up through their holes. You need a tool or long needle nose pliers with right angle to get them out.

At this point, it wouldn't matter if the head was a B18 or B20, you just need to find out what parts are there and what is causing the valve to stay open.
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'89 245 sportwagon, destroyed by hit & run driver, RIP. '04 V70 2.5 T Sportwagon, 12k mi and '91 245 5-speed, 209k mi, replaced the '89