Is my Oil pressure low? or is this normal?

[Dean'smeanmachine]

Hi all. i have a 72 Chevy truck with a 350 and the sm465 Trans. i have had this truck for going on 2 years. and am still in the process of a frame off resto.
the truck is now back together. well anyway i just changed out the old oil with some good 10w30 and a new Napa Gold filter. when its first start and cold the oil gauge reads a little above the half mark. then when i drive it a bit and it gets to operating temperature the needle drops between the half mark line and the other line before it at idle. when i touch the gas it goes right back up to the half mark and during accelerating and driving it all looks normal. its just the idle oil pressure that im concerned about.i did not have this problem with the old oil. the engine shows 63,000 more like 163,000 miles. i did not rebuild the engine during the rebuild because it runs perfect. is this normal or are my bearings going? or should i up the oil to 10-40 or 20-40? i really would like to be driving the truck this summer. An engine rebuild would be a big setback for me . Thanks for Any info in Advance..
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