With the tires and gears mentioned, you should be able to cruise 60mph at 25-2600 rpm. That's well within stovebolt capabilities.

Here's a spreadsheet if you'd like to play with tires, gears, rpm
https://drive.google.com/file/d/1tOJj5vmPHfJh61G5QV4-8iIjQ8WBDCB_/view?usp=sharing

Is the rear end actually 3.55?

'59 Chevy Suburban, NAPCO