55 TBIRD Engine & Tranny...what do I have

Bought 55 bird recently and it's now clear to me that I don't have the original engine and trans in it....engine looks like a Y block...how do I confirm that? And what size and year it is? Tranny is a smooth shifting 3 spd, only it's causing the engine to run at >3k rpm at 65mph...not good. How do I identify what it is as well? Thinking the tranny at the very least needs to be replaced with something that can run at lower rpm's at 70mph.



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