I searched around and couldn't seem to get a conclusive answer.
What is reasonable highway speed to expect out of my 272 (with 4 barrel) Lets guess shes around 200hp. This is backed by a T98 and a 3.70 rear end on 15in tires.

I found this site.
Gear Ratio Calculator

Which was kinda cool, but it says best i can expect is a top speed of 72, at 5800rpm which seems pretty absurd.

Truck handles surface roads just fine. Start in 2nd, moves though 3rd and seems to like to hang out in 4th at around 30-40ish? I have no tach or working speedo currently so its a best guess based on traffic around me.

Id love to drive her to work every once in awhile, but I am Leary to put her on the highway till i get a better idea. DC / Baltimore area traffic sucks... your either expected to do 70ish or is stop and go...

Ignoring the safety issues of the poor braking, and the fact iv got 3in of play in my steering box, before wheels even start to move...
Is it reasonable to assume I can cruse in 4th gear at 65mph if I right lane her?

To save anyone needing to look it up. Here is gear ratios.
1st 6.40
2nd 3.09
3rd 1.69
4th 1.0

 

Something doesn't seem right with your calculation. I run a Yblock with a 3.70 rear gear and 14" tires and it will do 72 mph easily but it isn't turning anywhere close to that rpm and no stock Yblock will without littering the hiway with pieces. I've since added an OD trans and it cruised 75-85 comfortably. I think your only option if you want to drive hiway speeds is changing your gear ratio to maybe a 3.25 - 3.50.

With your steering problem I wouldn't consider driving anything over driveway speed LOL

 

I have a 292, T-98 and had a 3.7:1 9" rear. It did take around 5000 RPM (I have a Tach) to get to 70. The engine was uncomfortably loud and concerning at that RPM and I never did it very long. I changed to a 3.00:1 rear and 70 is about 3500 RPM's now and highways cruising is no problem now. It also made 1st gear a usable gear instead of a granny gear, I do start out in first now almost all the time.

 

Either you are running 12" wheels or your speedo is off,those RPM'S are right for that gearing.
http://www.ringpinion.com/Calculators/Calc_RPM.aspx

 

The truck is put away for the winter, so I can't go check for sure and you may be right, I have not looked closely in a long time, it may be closer to 2500 than 3500. However what ever the RPM is, the 3.00 made the truck much more highway friendly.

 

Richmond gear has a nice calculator on their site. I have a T98 - rear gear was around 3.89 with 28" tires. 3268RPM at 70

 

Hooked up a temp tach yesterday to see what it was turning and this is just approx since my speedo is slightly off.

27" tires, 3.70 gears 3350 rpm at 70mph which is closer to 66mph actual according to those roadside electronic readout signs.

Second test in OD was 2695...

 

I figured out why my calculations were so off. I was only doing calculations with the "wheel size" and not factoring in the height of the tire. Stupid mistake on my part. Once you factor in 27in wheels. It makes a lot more sense and matches what you guys are seeing.

 

You'll be fine for short highway jaunts.

My 272 (2bbl) with the 4spd will top out at around 70, but it's much happier at 65, and I try to keep it at 55-60.

 

Yeah, I am much less worried about it now. I ordered a cheap digital tach, to get me by for now. The gauge cluster i want though is sadly about 800 for the set.. nothing quite like buying gauges that cost 22% of what i spent on the entire truck. They are going to have to wait for awhile.
These look great and rather fitting for her era IMHO.
Auto Meter - Gauges

I need to focus on the brakes and the steering lash. She stops but the parking break is non functional and since PO "rebuilt" the brakes right before he sold her, i am a bit worried.