What's the real deal on the 235 low pressure vice high pressure 235?

I've got an old low pressure 235 from 1951 with only 20,000 miles on it. It works great but wonder if I should be looking for a high pressure 235. The dash oil gage used to read 30max on the old six volt set up dash cluster but when I got the new one rebuilt by Chevy Duty it is now set to read 60 max. Does it really make any difference? How come and what is the difference between the engines?