The Bantams had 13 inch wheels and the Gamecock had 16 inch wheels. I think engines were different . Gamecock Humber Snipe 6 Cylinder and Bantam Humber Hawk 4 cylinder. Both were offered with Perkins diesels.
Gamecock
Gamecock E-series 3–4 ton 6-cylinder (1950–)Gamecock 14 seat coach and ambulance (1954–)Karrier-Walker 12 seat bus (1958–)Karrier-Dennis Ambulance (1962–)Ramillies refuse collector (1962–)Karrier ice cream van (c.1962)
Bantam
Bantam 50cwt (1933–34, 36–40)Bantam RSC road sweeper-collector (1933–39)Bantam F-series 2–3 ton (1948–63)Bantam FA-series 3–5 ton (1948–63)Bantam 4–5 ton tractor (1956–)Bantam tipper (1958–)Bantam FB-series 3 ton (1972–)
The Karrier Bantam, a Commer/Rootes Group product , enjoyed a very long production period. After the war the small lorry was fitted with a version of the steel cab that was employed across the range of lorries produced by Commer/Karrier at the time. By the early 60s the split-windscreen had given way to a one-piece version. Power for the Bantam was either a petrol engine from the group's Humber Hawk or a bought-in 4-cylinder diesel unit from Perkins of Peterborough. AFAIK both 4.206 and 4.236 versions were employed by the end of production in the early 1980s.