Seriously, don't convert one of those lotus touring frames. This isn't about the frame being classic or nice (though it is both things). The frame is a beast. The pictured bike is my old roommate's and it is still in my living room (and it is for sale too). Without any of the gear loading down the bike, the thing is impossibly heavy and most of the weight is probably the frame. Find something lighter and with less relaxed gemeotry.

And I think that bike is older then the 90s.