Interlace is inherent and automatic with an odd number of lines and correctly chosen H and V scan frequencies. A good way to explain it ito yourself is to draw the scan lines for a system with (say) 4.5 lines per field. Start at top left, then scan 4.5 lines, end at bottom centre. Fly back to top centre and continue, filling in the gaps as you go until you arrive at bottom right.
This page has useful info but there's nothing like trying it for yourself to get real understanding.
http://www.sparkysworld.co.uk/interlacing.htm
Non-interlaced NTSC can't really exist. If it's not interlaced, it's not NTSC. By definition. You can ghave a nasty kludge with 262 or 263 lines scanned 60 times per second, along with NTSC 3.58MHz subcarrier. The patterning caused by subcarrier in coloured areas will be truly horrible.