Here's another of those precise search terms that make me wonder how people arrived at this blog. They show up in the stats fairly often. Clearly this searcher was on a mission:
"derek bell porsche 917 monza 1971"
For fellow toilers in the vinyards of sports car racing history, I was going to suggest Time And Two Seats by Janos Wimpffen (1999). My copy gets used at least monthly to verify some factoid. Apparently it's out of print. Used copies are offered for up to $1200 (!) on the internet. But if you can find a library copy, it will answer questions like "What happened to Derek Bell and his 917 at Monza in 1971?" Maybe copies come up from time to time on eBay?
Time And Two Seats is a history of FIA sports car racing from 1945 to 1998. If the event was part of an FIA championship (including hill climbs), it's covered. The book is a monument of meticulous research. Each event gets a data table including race numbers, chassis numbers, drivers, qualifying positions, finishing positions, and more. Each event gets a narrative. Each year gets a narrative covering changes in technical regulations and trends, and a summary table of championship results. Each epoch gets an overview narrative. There are plenty of black & white photographs with sometimes humorous captions. Wimpffen writes clearly with occasional apt or funny turns of phrase. As you may guess, the book comes in two encyclopedia-sized volumes.
Rarely, I've seen a discrepancy between Time And Two Seats and some other (real or apparent) authority. Wimpffen's sources are the events' organizers' written records, and he took pains to resolve discrepancies he uncovered. Of course, written records can be wrong. But eyewitness testimony and personal recollection are equally if not more unreliable. My own confidence in Wimpffen's authority goes beyond "a discrepancy goes to Janos" to "the burden of proof is on the source that disagrees with him." Time And Two Seats is to FIA sports car racing as the Oxford English Dictionary is to English.