Chasing the vacuum leak

I never had the trouble getting one going right like you seem to be having but I grew up around engines and mechanics. That being said, all my Fords and all Fords I've seen always had a spacer under the carb. Perhaps the linkage is binding under the carb. Put the spacer on, with the four hole insert, and see what happens. The spacer will help keep heat out of the carb, especially if it's made out of a phenelic material. You will also need some longer studs.

I've not really been much of a gearhead before.  I am capable at fixing just about anything body or suspension/driveline related such as axles and what not....but when it comes to motors and transmissions I'm not afraid to admit I am clueless.  Willing to learn, and love to get my hands dirty, but clueless all the same.  Especially since this is my first carburetor.  I greatly appreciate forums like this for that very reason.

This thread was me January 2018 and I've been through everything you've described. In fact it's almost identical save for the 4Brl as mine is a 2 and I'm about to replace the intake manifold ! Got the coolant drained today and all bolts loose without snapping one thank goodness !!!
 Anyway I'll check back in this weekend hopefully.  Good luck

Yea I feel like an idiot now, turns out the choke not being connected on the hot side is a whole other problem with the high idle.  Yes the vacuum leak was somewhat responsible but the choke staying closed is the last bit of the puzzle.  Tested today by letting it warm up and manually opening up the choke notch by notch by pushing the blade and clicking down the red handle.  Idle immediately came down, and ran like crap until it sputtered out.  So yay idle fixed finally, now time to tune the mixture screws and get it idling pretty.  Once the idle dropped, this motor sounds like it's cammed.  The lobe is pretty mean.  This is my first 351 so maybe they all sound like that with minimal exhaust piping (mine exit out of the side) but it's a low roller for sure.

We've all done it, made some mistake that when we look back seems so obvious.  So, you aren't alone.

I'm just glad you peeled another layer of the onion.  Yeah, you probably have more layers to go, but you'l get there.

As for the idle, it didn't sound like it had a lope to me.  But, you can induce a lope with a bad idle air/fuel mix.  Lean seems to do it most easily and the engine will almost die and then come back again.  So maybe what you are hearing is just because the idle mix is off.

Yea I actually located the hot wire meant for the choke laying down under the radiator, the previous owner was in process of pulling the motor and had disconnected everything with no specific order involved.  Ended up rewiring that proper, and I also discovered another issue in the process of doing that.  The truck had been very slow to crank especially when hot.  The chassis ground was all sorts of dirty with corroded wires/rusted connectors so I cleaned the mount up and rewired that as well...cranks are timely now so that is also good.  Lots more to go but I am just glad to finally be on track with the motor.

Next thing I plan to tackle is cleaning out the interior, knocking out some of the surface rust here and there on the inner dash frame while the dash is still out.  Wire up the gauges a long with the rest of the interior, bunch the harness back together and tie it up, repair the bench seat upholstery, then begin tackling the exterior.  I am excited though, really looking forward to the upcoming weeks worth of what I consider fun work with the motor finally coming along.

If only I were that lucky