See that hole at about 6:30? Is there any blockage over or in it? Can you blow compressed air through it? That is the drain of excess oil back to the sump.
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Do you have another spring which is shorter than the one in there now? If so put it in, start the engine and notice what the oil pressure does. If it doesn't come up at all of course shut it down. If it makes no difference, then try removing the spring all together and try again. If there is still no difference then the drain is blocked somehow and a replacement relief valve assembly will do nothing for the situation.
Increasing oil pressure is usually not an issue. Normally one gets worried when the pressure goes down. The only time that I've seen high oil pressure in a Lycoming was in an Enstrom helicopter during cold weather start up. Then it was just a matter of letting the oil warm up a bit until the pressure came down.
What are you using for oil? You didn't happen to put in some W120 or SAE 60? That could do it.
Another thing you could check is with the valve removed as in the picture, pull the prop through by hand or crank with the starter. Does oil flow out of that center hole? If not there is some internal blockage somewhere.