It's an Alexander AL body. The AL/Atlantean AN68 was the standard bus from 1972 until this batch was delivered in 1981 (and had been preceded by earlier versions of Alexander Atlanteans since the first in 1966 - in total ECT and Lothian took almost 600 over 15 years). Lothian moved on to ECW-bodied Leyland Olympians after this.
588 Atlanteans in all - 225 PDRs and 363 AN68s.
PDR1/1, Alexander A H43/31F: 801-825, 851-899 (ESF801C, EWS802-825D, JSC851-899E). New 1965-67.
PDR2/1, Alexander J H47/35F: 900 (JSC900E). New 1967.
PDR1A/1, Alexander J H45/30D: 301-350, 351-400, 251-300 (PSC301-350G, SSF351-400H, WFS251-300K). New 1969-72.
AN68/1R, Alexander AL H45/30D: 1-50, 901-950, 401-464 (BFS1-50L, OFS901-918M, OSF919-950M, GFS401-450N, JSG451-464N). New 1972-75.
AN68A1R, Alexander AL H45/30D: 465-620 (MSF465-500P, SSG501-560R, YSF561-575S, JSX576-598T, OSC601-620V). New 1976-79.
AN68C/1R, Alexander AL H45/30D: 621-659 (GSC621-659X). New 1981.
AN68C/1R, Alexander AL H45/31F: 660-665 (GSC660-665X). New 1981.
802-825 had short bay windows, all others were panoramics.
465-665 were fully-auto, G2 on 465-598 and 601-620, LVA45 on 621-665. All others were semi-auto. 901/2/42/6-9 were converted from semi- to fully-auto by ECT when new, on withdrawal their gear control systems were fitted to 448-454.
561-575 were originally to have been registered SSG561-575R.
660-665 were to coach spec (albeit with bus seats), hence the single door.
900 was the sole 33ft Atlantean to be purchased by Edinburgh. All others were 30ft long.