I did a search for this info but I got a lot of back and forth answers from past posts. Would it be better to run 390 heads on the 365 block, do they flow better, bolt right up without problems?? Also, I saw that Eelco sells a trans adapter to a gm manual but it is for a 331. Does anyone know if it will bolt to the 365?? The bolt pattern looks the same minus the top center bolt (kinda near the distributor). I know that wilcap sells an adapter to link anything thing to anything, if that is my only choice then that answers that question Any help would be appreciated.
I have a '56 365 engine in pieces, and recently picked up a set of '60 390 heads. The valves are set farther apart, making room for bigger valves yet. I believe if you do the swap, you have to use the 390 pushrods ( makes sense, I guess ). The ports appear to be the same size, BUT, looking into the siamesed exhaust ports, the 390's have a cast-in par***ion, to better direct exhaust flow out, rather then toward the other port. Kind of like when folks weld-in port deviders in center flatty exhaust ports, or other engines with siamesed ports. I can't help but think the caddy engineers came up with this to increase efficiency. Other then the pushrods, the heads should be a straight-across swap. FWIW the '60 p***inger side exhaust maniflod is a nice looking "rams-head", center-dump.Later ones have fins cast in,not so clean looking.
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