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You have a 4 speed OD trans, right? All four gears shifted with either a tower mounted or side mounted shifter?
This trans has the same bell to trans pattern as the old toploader. Double check the pattern, and measure the input shaft length, pilot bushing size and spline. My guess is it bolts on as-is.
Bell to engine on the 300 six is the same as the small block 289-351w motor. FE is different.
So, you are probably in business....
If you don't want to disassemble, check the bell housing depths, which will give you a strong hint as to input shaft length being equal or different.