There are two batches of the letters you refer to. During the 1951 model year sales drives, Kaiser-Frazer Sales Corporation rolled out the program & brought it back in 1953. The company contracted with an sales stimulator company to do these and dealers could order the materials with their name already imprinted as shown in the 1951's (along the bottom edge & at points in the letter body).
The ones I have are:
1951 1953
High-Powered Pride of Willow Run This Will Last!
Take off the Blinders The World's Safest Front Seat
Who Wouldn't Be Cozy? More than meets the eye! (Kaiser & HJ shown)
If you could see our file Rugged as a Penny (HJ)
Let's ask ....(letter to the dealer requesting feedback) The Longest Ride per gallon (HJ)
ALL KAISER THE FIRST 2 ARE KAISER ONLY
1951's are b/w photocopies personalized for Maple City Motors; 1953's are originals in color with no dealer reference.