An update on my rear end swap-- I am done! I completed it this morning. I had been waiting for my new drive shaft which I picked up last night. Installed it this morning and went for a test drive. No vibration, no shaking, no growling or howling! It rolls down the road at 55 mph just fine. I have not checked the RPM yet, I have to attach my timing light that shows the RPM and go for another ride but listening to the engine, it does not seem to be to high of an RPM. My goal was to be able to cruise at 55, and I think it will. By my calculations, the RPM should be about 2600 at 60mph. If my RPM is a little high at 55, my next idea is to put taller tires on it. It currently has 27 inch tall tires which I know is a little short but they look good, I have read that the stock tire was 31 inches tall. Previous owner put these tires on with 15 inch rims.

Any suggestions on an acceptable cruising RPM? I am not cruising for hours upon hours at highway speed but I don't want to abuse it.

All in all, I feel this swap was worth it, I enjoyed doing it, and so far it seems that it will work fine.
Thank you to all that give tips/advise/suggestions! It gives us new guys a little more confidence.

 

I am glad to hear it worked out for you. I did the same in my truck and along with a complete rear suspension rebuild it was a night and day difference. All of that extra work with the pinion angle was really worth it for you.
Not sure which engine you are running or what your new rear end ratio is. But if you are spinning 2600 with a non overdrive transmission at 55 MPH it sounds like your in the right neighborhood. I have an old school non overdrive Ford FMX transmission (autos will chew up a little extra RPM) with a 3.54 rear. Using 27 inch tall radials I run 55 at 2700 RPM.

 

I have the original (rebuilt) flathead V8, the original 3 speed transmission, and the 9 inch rear end is now 3:50, tires are 205/75 15 inch rims. Both the front and the rear suspension now have all new pins and bushing in the leafs/shackles. I am waiting for the rain to quit so I can go for another ride and check the RPM. Being a non overdrive, I will probably be about the same RPM as you being the tire size and ratio are the same. I know my ear is not calibrated very well for RPM's....
I will update when I have more info.
Thanks for your input, I appreciate it.

 

Well I was able to get it out in between raindrops. I used my timing light that displays the RPM, I expect that is as accurate as anything else would be. At 55 mph it is running 2450 RPM, at 60 mph it is at 2690. I am new to flatheads, but from what I have read on this forum, I think it should be fine cruising at 55 mph in that RPM range.
I am sure I will be looking for more tips and advise as I work my way around it and other stuff to do to it.