look for 265 valve covers not just 283, you might have more luck. the earliest v8 was the 265 and had the staggered pattern.
i caught an ad for some aluminum 265 vette valve covers on the list of craig for $50! I was the first to call and after some careful questioning, do i know what year these came on, do i know what motor these fit, etc, he invited me out to pick them up. he had an all original 55 vette with a 327 he just installed and the original 265 on the stand with the factory stamped steel corvette valve covers. beautiful car and I understood why he was being careful about coming to his house. he had a 67 camaro and a 51 ford f1, everything was super well kept and original (except the 327 in the vette)
edit: first google link, steel, but i bet more searching will find aluminum
https://www.jegs.com/i/RPC/707/R9214/10002/-1