Since 1' = 12'', so the scale 1/4'' to 1' is 1/4'' to 12'', or, multiplying both sides by 4, 1 to 48.
Convert all dimensions given from foot/inches to inches, then scale them down, dividing by 48.
10ft 6in=10*12+6=126+6=132 dividing by 48. 132/48=2.75/48=0.0572*1000=57.2 inches
18' 8'' = 18 * 12 + 8 inches = 216 + 8 = 224 inches. Dividing by 48: 224/48 = 4 32/48 = 4 2/3 inch*1000=66.6