Yes, remove the intake elbow and watch to see if fuel wells up around the needle when the piston is manually pushed up. This will indicate a sunk float OR stuck needle, both of winch require the removal of the carb to check/ rectify.
Is it a low or hi compression 4.6? the 3.5 heads are OK at low engine speeds, the restriction of smaller inlet ports will help a little RE gas speeds. Best thing to do though is port match as best you can, especially exhausts. Who wants/ needs to run a carb 4.6 at 4000rpm anyway:o:twisted:
JC

