When I started building my Murray cruiser I was as concerned about the length as I was about height. I'm 6'2" and needed more space between the set and peddles without raising the seatpost a rediculous amount. I solved the problem by stretching the front out 4" with a springer, and added about 4" to the rear with beefed up axle mounting plates in place of the knockouts. To take full advantage of the additional length I moved the seat back several inches to extend the distance to the pedals. It's much more comfy
and seems to handle better. Some folks extend the wheelbase by cutting the frame and welding in longer tubes. I'm such a lousy welder, that option would have meant days of grinding!!