I had real similar luck with an old 230 in a 65 nova I had, single barrel. Seemed like nothing I did could get it to run right over idle...if I could even get that. Original carb, rebuilt it, would go too rich to where exhaust manifold would glow from exhaust overtemp just trying to get damn thing to run. Replaced whole ignition with no luck, adjusted valves, fuel delivery to carb checked out, couldn't find any vacuum leak. Leakdown test on cylinders was not the greatest. I never did dig into the timing chain, but suspect something was not quite right in there because would end up raw fuel dribbling out exhaust sometimes. Finally end up selling it since it was a free car and 4 door just to get it out of my hair and give me time to mess with my 2 door 64 instead, lol. About all I figured was v-8, 4 barrel and HEI was alot easier to troubleshoot than that damn setup for sure. If engine mechanical is sound, it's basically spark or fuel problem that I would start with spark, verify complete ignition, then work on the fuel. Since an engine is just an air pump, verify no intake restrictions and same with exhaust since I've had a rat's nest inside a muffler before blocking off air flow so severe backpressure.