273 vs 318

basically agreed here but with one exception, the 360 head (non magnum)head flow is a very small number off on stock 340 head. the main diff in these heads is the intake valve, 202 for 340 till 72 were it was changed to 188, 360 heads were 188. 1970 340 head actually have 360 cast on them on the intake runner were 68-69 had 340. the casting number were the same. not sure but i believe T/A heads have the same casting number but a diff part number. the flow numbers between 202 and 188 heads are a diff of 5-10 cfm difference give or take. the good news for the later smog 360 heads is that the exhaust has a slightly raised floor because of air injection and these port flow higher then 340 heads

From what I've read the 2.02 X/J flow about 20 cfm more than 1.88 heads. And a 360 has 20 cid more to feed which needs about another 15 cfm more than 340's 2.02 heads to put it in the same cfm:cid ratio as 273/340. Just to put in perspective a 408 and 440 to be in the same ratio would need 260 cfm and 280 respectively or basically eddy heads.