I know a guy who put a 69 k frame in a 64. It sets the engine back a bit. There are a few considerations:
Good:
better weight distibution
common 66-72 oil pans all fit
common 66-72 headers all fit
more clearance for fan clutch
common 66-72 B or C body engine mounts
better thru bolt idler arm

Bad:
kickdown linkage interferes with heater hoses at firewall
trans mount needs some modifying.
Manual trans cars need clutch linkage reworked
driveshaft needs shortening
Max Wedge manifolds now interfere with firewall
stick B engine ex manifolds might not clear.

I guess you should take everything into consideration and see if it will benefit your situation