Blimey. I reckon it would be from 1966, after the switch to 3-litres. Let me have a look...
OK, Spa 1966 had:
3-litre Ferrari V12 (Ferrari)
3-litre Maserati V12 (Cooper)
1.9-litre BRM V8 (BRM, Lotus)
3-litre Repco V8 (Brabham)
2.4-litre Ferrari V6 (Ferrari)
2-litre Climax V8 (Lotus)
2.8-litre Climax L4 (Brabham, Eagle)
3-litre Serenissima V8 (McLaren)
3-litre BRM H16 (Lotus)
...I think that boils down to seven different configurations/capacities: 3 V8s and a V12, V6, L4 and H16.