I used an engine pre-luber to circulate oil before firing the engine up.  It looks like a propane tank; put a quart of oil in it, add some compressed air, and hook it up to one of the oil pressure ports.  Open the valve to get the oil going, then spin the engine over by hand.  All of this is after making sure the fuel tank has good gas in it.

There are several youtube videos showing how to do this.  You'll need a vacuum source, such as a Mityvac hand pump.   https://www.youtube.com/watch?v=SZtDhOgdxno

Do you have the correct high-riser rocker shaft stands?  The high-riser requires a shorter stand than the low and medium riser heads.

Dumb question for you....  What kind of readout does your digital scale have?  Is it a 7-segment LED display?  If so, is the lower left vertical segment on the "hundreds digit" burned out?  Missing this segment would turn an 8 into a 9.....

Never been in anything "vintage" at speed, but I've been in plenty of fairly new vehicles at speed.  I neither confirm nor deny that I've been in both an SN95 Mustang and a New Edge Mustang at over 140 mph.  I also neither confirm nor deny that both cars handled very well, but the windshield wipers were beating the windshields to death. 

Just as an added quip, I got to drive a Busch series car around Charlotte and at 135-140 mph, I could wiggle my foot and the car would instantly respond and accelerate.  It was amazing.

Sounds like you've unofficially had some fun on the street and track! 

How fast you CAN go, of course, depends on available rear wheel horsepower and proper gearing.  Drag horsepower increases with the cube of the velocity whereas rolling resistance horsepower is proportional to the square of the velocity, so it adds up quickly.  I've run the numbers for my 70 Mach 1, which has a 454 cid sideoiler delivering approximately 400 horsepower to the rear wheels.  For a Cd of 0.52, frontal area of 20.2 square feet, and a weight of 3750, I calculate a top speed of about 170 mile per hour.  The fastest I've ever driven the car was 130 mph and I wouldn't want to go much faster than that.

Tunnelwedge, are you really planning to tow the trailer with your Mustang?  Should have plenty of power! I assume you've done some frame/chassis mods?  Mine weighed about 1600 dry, maybe 1800 fully loaded and it had a Torflex axle with 7" electric drum brakes.  I towed it with a 2004 Sport-Trac, a 2011 Honda Ridgeline, and my 2018 F-150.

Very nice and a fun project!  I built this one in 2006 but she has "grown" into an Airstream as my wife wanted a bathroom.  We gave the teardrop to the kids so they could "join us" but not really join us.....