Charlie/ Phillip H. - hope you find this cause I had a 'senior's' & said 'Lincoln'. (Just testing your adaptability!!).
Mfg date by my reckoning from Oscar's book is-
C = March
23 = 23rd
8 = 1998
G = Brownsville plant
In Cub Cadet Parts Lookup type in model 1720, then select range of your serial no., & off you go.
Service Manual - I have 1 on the way from Binders. Charlie, I think I have said earlier, I tried the great MTD site you gave me, but it was a no go for 1720 Service Manual.