There are no known Skowhegan records available so I can only help you with a Kennebec identification. Many of the Charles River area builders also used a similar numbering system so it may not be a Maine canoe at all. None of the records are known to exist for any of the Charles River canoes either.
The Kennebec serial number 506 went on a Yankee Flier boat in 1928. They often would assign a 100,000 series number to their Kineo Special model canoes and only stamp the last few digits on the canoe. Their number 100506 was assigned to a 16 foot long canoe which doesn't match the trailing 17 on yours. Their number 101506 is a 17 foot long canoe so please check the length, verify the numbers, and let me know which record you want. Thanks,
The Kennebec canoe with serial number 101506 is shown on page 238 of volume four in the Kennebec ledgers. This was assigned to 17 foot long Kineo Special Model. It was planked by Morgan on March 19th, 1927. The canvas covering was applied by Roy on March 26th, 1927. The first filler coat was applied by Grant on the same day. The second filler coat was applied by Roy on April 23rd, 1927. It was railed by McInnis on the same day. The original color was yellow. It shipped on April 25th, 1927 to location "27-79" with three other similar models listed on the lines above this one. This location is probably an order number but we don't currently have enough information to identify it.
The scans of this build record can be found by following the links at the attached thumbnail images below. These original Kennebec records are reproduced through the courtesy of the Maine State Museum.
The microfilms and scans of these records were created with substantial grants from the Wooden Canoe Heritage Association (WCHA) as you probably know well. I hope that you will join or renew your membership to the WCHA so that services like this can continue. See http://www.wcha.org/wcha/ to learn more about the WCHA and http://www.wcha.org/join.php to renew.
The Kineo Special model shown in the 1927 Kennebec catalog with a middle thwart and was not a fancy courting canoe that would be likely to have the "Oval" shaped outer stems or distinctively shaped thwarts which you mentioned. This sounds more like a Charles River area canoe so some pictures might help identify it if you can provide them.
It is also possible that you could have another number or manufacturer if this description doesn't match the canoe. Feel free to reply here if you have any other questions.
Sure looks like Charles River- thwarts, ribs, "chubby" outside stems. I was thinking this was a Nutting, but not so sure now with this better deck photo. Nutting used multiple deck styles, but I'm not sure about this one. The owner told me this canoe has variously been identified as Morris, Kennebec, Old Town, etc.... odd. Doesn't look at all like these builders. Charles River-area seems much more likely. "506 17" would be an appropriate serial number for a CR-area canoe, and it wouldn't have had a center thwart with these two wide thwarts (typical of CR-area canoes). The specific style of these thwarts (not just the fact that they are wide- a number of MA, ME and other builders made wide thwarts) is characteristic of those from more than one CR-area builder.