Jim,
Here is an RR track volume 4 version bitmap of a Lionel Fastrack 072 reverse loop. Each block in the photo is one foot. Click on the photo to get the true size its abit compressed as shown below. Just remeber your train has to fit the reverse loop & not to long or it will hit itself as it returns out of the loop. As noted this uses an 072 wye switch. Hope this helps.
NUMBER DESCRIPTION
(3) FasTrack 1.38 inch fitter
(2) FasTrack 4.5 in straight 12025
(2) FasTrack O72 11.25° curve 12055
(16) FasTrack O72 22.5° curve 12041
(1) FasTrack O72 wye switch 12047
Total of 24 items
George