about engine swap

No real advantage of a 340 over a 360 other then less cubes and you'll pay much more for a 340 then a 360.

360's are plentiful and easy to find can build it up the same way. Only differences are the oilpans and the fact that the 360 is externally balanced where as the 340 up to 71' is internal balance the 72' 73' was external balance.

price out a 360 and a 340 and decide what you want both will proform great if built right