Although Nasty and a few other sites show this only in '69 as a B-Body code, if the original and/or a '68 HH it's a 327/250 Hp 4bbl w/ a 2 speed Powerglide.
Here's all 1968 B-Body Chevrolet Suffix Codes below from Impalass.com...click here for Rpo's etc
http://www.impalass427.com/68RPO.htm
~ Pete
CA, CJ, CM - 250 c.i. I-6, 1 bbl, 155 h.p. 3 speed manual
CC, CK, CN - 250 c.i. I-6, 1 bbl, 155 h.p. 3 speed manual with A/C
CQ - 250 c.i. I-6, 1 bbl, 155 h.p. 2 speed Powerglide auto trans.
CR - 250 c.i. I-6, 1 bbl, 155 h.p. 2 speed Powerglide auto trans. with A/C
D0, DQ - 307 c.i. V-8, 2bbl, 200 h.p. 3 speed manual
DP - 307 c.i. V-8, 2bbl, 200 h.p., 4 speed manual
DH, DR - 307 c.i. V-8, 2bbl, 200 h.p. 2 speed Powerglide auto trans.
DK - 307 c.i. V-8, 2bbl, 200 h.p., Turbo Hydra-Matic Auto Trans TH400
DS - 307 c.i. V-8, 2bbl, 200 h.p., Turbo Hydra-Matic Auto Trans TH350
HA, HB - 327 c.i. V-8, 4bbl, 250 h.p. 3 or 4 speed manual
HC, HG, HH - 327 c.i. V-8, 4bbl, 250 h.p. 2 speed Powerglide auto trans.
HF - 327 c.i. V-8, 4bbl, 250 h.p Turbo Hydra-Matic Auto Trans.
HI, HL - 327 c.i. V-8, 4bbl, 275 h.p. 3 or 4 speed manual
HJ - 327 c.i. V-8, 4bbl, 250 h.p. 2 speed Powerglide auto trans.
HM - 327 c.i. V-8, 4bbl, 275 h.p Turbo Hydra-Matic Auto Trans.
IA - 396 c.i. V-8, 4bbl, 325 h.p. 3 or 4 speed manual
IG - 396 c.i. V-8, 4bbl, 325 h.p. 2 speed Powerglide auto trans.
IV - 396 c.i. V-8, 4bbl, 325 h.p. Turbo Hydra-Matic Auto Trans.
IE, IH - 427 c.i. V-8, 4bbl, 385 h.p. 3 or 4 speed manual
IJ, IS - 427 c.i. V-8, 4bbl, 385 h.p. Turbo Hydra-Matic Auto Trans.
IC - 427 c.i. V-8, 4bbl, 385 h.p. manual, police package
IB - 427 c.i. V-8, 4bbl, 385 h.p.Turbo Hydra-Matic Auto Trans., police
ID - 427 c.i. V-8, 4bbl, 425 h.p. Special High Performance (manual only)