You can probably put a set of 650c wheels on the LHT, depending on how much adjustability you have in the height of the brake pads. But every time you switch from 26 to 650c, you'll have to adjust the brake pads up or down. If you have canti brakes, this might be more than you want to deal with. Alternatively, you could run 26" rims with narrower tires, but 26" rims don't come as narrow or light was 650s. There's a chart on Sheldon Brown's site that will allow you to judge how narrow you can go with tires based on the width of your rims.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72