To no avail as he DNF'd after one lap with a fuel leak and subsequent fire..

"Concerning Cunningham's Tipo 63 at Riverside 1961.  Little known info: Toward the end of the week while practicing, Augie Pabst blew the engine, which was a 2.8 liter V12. Cunningham had another 12 in a box and he and Momo talk it over and decided to replace the blown motor. It turned out the replacement 12 was an experimental 2.5 liter 12 with desmo valve action originally designed for the 250F Maserati Formula One car, but the Maser boys found that the old reliable six ran better, more reliably than the complicated 12 plus it handled so much better. So they elected to sideline the desmo 12. 

The problem we had when exchanging engines is the engine we removed was either 60 degrees or 65 degrees (between engine banks) and we had one hell of a time mounting the engine. We started around 6 pm Saturday nite until around 5 am Sunday (race day) to get the engine installed. When we fired if off, it "shrieked", the wildest sounding thing you ever heard. We had to re-jet the Webers, Momo poured out jets into my hands and expertly replaced the jets in the Webers..... 

Momo had to drive the car to RIR because we had no time to load it into the van and get it to the track.  As I remember it, there was a 20 or 25 lap race fairly early in the morning for big bore cars who had not qualified earlier and the top four or five would then run in the main event. Pabst took an easy first or second and consequently made the grid for the main event...

For that race, Phil Hill didn't have a ride and drove a unique Pontiac with the trans mounted at the rear end and a flexible drive shaft at around 50 mph as a pace car and for the crowd to photograph the race cars at slow speeds. 

Well, our Maser did not have a tractible cam curve, made for Formula One racing it had a narrow RPM range, all the power was up around 6M-7M RPM and Pabst had to constantly clutch the engine keeping the revs up or it would foul out the plugs.  As it turns out, in the process of keeping the 12 running by revving the engine it backfired several times and with the rich fuel mixture, it caught fire.

On the long mile+ back straight, Pabst pulled away from the pack and tried to snuff the fire by driving fast... It didn't work. He stopped at the end of the pits with the back of the Tipo 63 in flames. Problem was, part of the car's metal work was Magnesium.  We finally got the metal cool enough with foam and the fire went out. But by then much damage was done and we were out of the race.  I was so tired, I went inside one of the vans and fell asleep, waking up just in time to see the Australian driver Jack Brabham winning the event."

Is the man in the pith helmet riding aboard, or walking beside, the obviously crippled Maserati?

"The Tipo 63 Maserati on your site is chassis 63010, not 63002. The latter was the original Pabst car planned for Riverside, with its engine still in a wooden box after last-minute work in New York. However, chassis 63002 was not used that weekend. The boxed engine 63002 went into chassis 63010 [after engine 63010 blew up in practice] and that is the combination that Pabst drove, however briefly."

In this reliable and  well-sorted car, he finished both events.