The summer event which last year took place in July is no longer. I know not of any other opportunities to race a historic single seater at Spa apart from an FJ at 6hours but could be wrong.
So far as accidents are concerned EddyV I don't agree. There has been endless discussion about the accidents in closed wheel races at the 6hours meeting on this forum, and the cause attributed to tyres, spec of car and woeful driving from what I can interpret. There's no rememedy for drivers brain fade however I think there's an argument to say there's less crashes in single seaters because the drivers have a lot more respect for each other as any contact usually ends up with more severe consequences than with closed wheel cars.
That's not to say accidents don't happen of course. I lent my own car to my dear uncle in 2002 which resulted in him being ambulanced to Liege hospital with broken ribs and burns, and no it wasnt raining.