[Dave in MN]

Bob,
From my experience the cost will be close to $7,000.00.

Be prepared to replace the "B" block if you plan to build the power and speed by upping the engine RPM only. IMO: The weak spot in the Model B engine is with the exhaust ports. If you develop the HP necessary to run the car down the road for long distances at the speed you describe, the block will likely fail at the exhaust ports. An overdrive will greatly reduce the heat load on the engine/exhaust valves ports and bring the RPM down so the ride will be more enjoyable.

I have two cars and engines capable of 60-65 all day with the occasional burst to 75 if necessary. Both have overdrives. The one with the "B" engine is on its second block.
FWIW: It is never enjoyable driving at any speed over 65 MPH in either car. Too loud and the front of the cars get pretty light at speeds over 70 MPH. At 75 mph and over it gets scary. The wind gets under the front fenders and reduces the front sprung weight. At this point/speed the steering gets real easy, like you were riding on air. At those speeds I think you partially are!
Please be careful.
Good Day!