The car that Jimmy Clark raced in the 1963 Indy used a 256 ci pushrod v-8 that used Weber carburetors and ran on pump gas. He came in 2nd behind Parnelli Jones, but he should have won as Parnelli was leaking oil and everyone behind him was forced to slow down as there were a couple of spins. It was a controversial finish and kept the race and Ford in the news for awhile.
No one but AMT has made a kit of this car and they also did one of Parnelli's in the mid-60's and they were very detailed kits for their time with detailed engines and suspensions. These were re-released in a 3 car kit of Indy cars during the ERTL years, but if you can find the early AMT kit they had vinyl tires rather than the plastic tires in the later kit. These pop up on the 'Bay every once in awhile for reasonable prices. The other kits mentioned are pretty far from the Indy Lotus.
I was working on this during the 500 but hadn't finished it. It's nearly there. Here's my 1963 Lotus powered by Ford:
Here's a group shot with the Jones Offy:
Hope this helps,