I agree with It1s10.
2800 rpm shouldn't hurt.

I run my 462" Buick at 3000 rpm at 70 mph on the desert highways.
Sometimes up to 3200 rpm on a 5-10 mile run.
Speed limits here are 75 mph on many of the desert highways.

The big Buick engine is fairly short stroke (3.9") all things considered.

Any chance you could go to a 28" tire?
That would get your rpm down about 5-7%.

Mph = rpm x tire diameter divided by 336 x axle ratio.

You can roll things around in the formula to decipher your axle ratio.


Or . . . you can mark the driveshaft, mark the tire, roll the tire one revolution and count driveshaft revolutions.
EG: tire turns once, driveshaft turns just a touch over four indicating a 4.11 or so ratio.
This is pretty accurate if you pay attention.

Use your head as well.
Don't get under the car to do the counting, you should be able to do it from the side.
A couple of helpers, one behind the wheel to operate the brakes as required and one to push the car - engine off - will make life easy.
Safety first above all other things.

If you don't have a locking differential, you can jack up one rear wheel, rotate it one turn and count driveshaft revolutions.
EG: a small amount over two driveshaft revolutions indicates a 4.11 diff.