Hi there,
In the 1850s, “Old Bowenfels” was ummm….. not known as “Old Bowenfels” but simply as Bowenfels. When the Railway came, then one of the stations on that line was named Bowenfels, and so, the original settlement became known as Old Bowenfels, and the settlement around the Railway became known as Bowenfels. However, the railway did not get to Mt Victoria until 1868, to Wallerawang in 1870 and to Bathurst in 1876. So in the 1850s, it was simply Bowenfels. The road we all know as The Great Western Highway, was once known as The Western Road. And back in the 1850s, I think you will find that at Hartley it headed off towards O'Connell rather than off up the River Lett Hill.

I have made some notes from Grevilles 1875 PO Directory:
BOWENFELS
A township in the police and electoral districts of Hartley, county Cook, on the Western line, is 100 miles from Sydney. The township is 3000 feet above sea level, three miles from Lithgow, and lies in the valley at the foot of the Zigzag.
HARTLEY
A township in the police and electoral district of Hartley, county Cook is 83 miles west from Sydney. The township lies about five miles south of the Great Western line of railway. Hartley lies in a valley amid the peaks of the Blue Mountain range, 2300 feet above the sea-level.
LITHGOW
a settlement and station Great Western line of railway, 97 miles west from Sydney.
Here’s some further info that may be of interest.
1880s Railway timetable….
Mt Victoria, Hartley Vale, Mount Wilson, Clarence Siding, Eskbank, Lithgow, Bowenfels, Marrangaroo, Wallerawang, Rydal, Sodwalls, Tarana, Locksley, Brewongle, Raglan, Kelso Bathurst. (Change at Wallerawang for the Mudgee Line).
The Distance from (South) Bowenfels to Wallerawang via the roads in the 1850s was far more than 12 Kms. For instance, it was only in the 1930s that the Forty Bends Road (around the foot of Hassans Walls), diversion was made. From Hartley to Wallerawang

, in the 1850s

, may I suggest the Western Road from Hartley did not go to Wallerawang ..... likely it would have been West via O’Connell and then north into Bathurst So back then, enter Bathurst from the SOUTH and not from the EAST. And following on from my “tape measure” comment, I have found a Wiki page that others may find interesting.
http://en.wikipedia.org/wiki/Great_Western_Highway McKane Falls Road runs to/from from the intersection with Jenolan Caves Road, to the Great Western Highway at South Bowenfels. . It is about 7 ˝ kms in length. May I mention that from there to Wallerawang Railway station according to Google Maps it is about 17.85 kms
http://www.gnb.nsw.gov.au/place_naming/placename_search/extract?id=anYbBKKmGH Mckanes Falls are on the Coxs River, south of Old Bowenfels and about 2500 metres east of Mount Blaxland.
From the intersection of the Great Western Highway and McKanes Falls Road, South Bowenfels, travel 11.4 kms west on the GWH.
Take the Castlereagh Highway exit 850 metres
Travel on the Castlereagh Highway 4 Kms
Turn left onto Main St and travel 1.6 kms, you should be at Wallerawang Railway Station.
11.40
00.85
04.00
01.6017.85
It should have taken you about 17.85 kms according to that tapemeasure

.
Civil Parish Maps
http://www.lpi.nsw.gov.au/ (Mapping and Imagery, Historical research etc)
http://www.lpi.nsw.gov.au/mapping_and_imagery/parish_maps http://www.lpi.nsw.gov.au/publications/search_guides http://www.rootschat.com/forum/index.php?topic=538663.0 Now to get on with looking for McKenna for our OP
ADD
One of my rellies has just phoned and reminded me that initially during the Convict era, the locality was known as Bowen Hollow and it was a minor Convict Stockade in the 1830s

....
http://www.comleroyroad.com/convict-stockade-bowens-hollow.html http://www.tablelandsway.com.au/news.asp?id=10&pid=21 http://trove.nla.gov.au/ndp/del/article/12857406 smh 20 Sept 1839 (Capture of Bushrangers beyond Wallerawang, by the Bowen Hollow Police Sgt, and locking them up at Hartley)
http://www.rootschat.com/links/0zco/ pdf with historic info, maps, etc
Cheers, JM