Classic/Antique Car Repair: oil pressure loss, oil pressure gauge, check oil level

Question
    I have a 1954 chevy 210 with a 235cu.in. motor that was just rebuit I have just 700 miles on it,changed out the breakin oil and put in 4.5 qts. valvoline 30wt. sae motor oil and a oil additive.Drove it here and there everything running fine,oil pressure is fine,cooling system fine,carburater is fine,vaccume advance disconnected because of diapharm,tire pressure fine,brakes are fine.Finally ready to take off for the coming holidays and get on the road for my 400 mile run. But first I thought I would get on the freeway and take trail run. Going 55-65mph in the middle lane everything seems to be ok for this 25 miles,all of sudden I smell oil Ilook down at the oil pressure gauge and Iam lossing oil pressure. Got of the freeway and parked it.Let it cool for hour,check oil level it was up but added a quart thinking it would make the oil thicker.New fuel pump,took a lighter and put a flame to dip stick,nothing,now Iam being told to try a 20/50wt.motor oil.Yes I made it back with some oil pressure put at low rpm there isn't any.LOOKING FOR HELP AGAIN THANK YOU DAN&DEB.

Answer
If the engine clearances were set up right on the money 30W motor oil is way to thick to get though the small clearances between the bearings and the shaft. This can burn out the bearings even though there is oil getting to them. With today's oils and the machining that we use today a 5W-30 in a fresh rebuild should work well. Time to pull the pan and check the bearings. I doubt that you will get the pressure back without work. Let me know what happens.
Brad