i would think long steady interstate travle would be alot less punishing than stop and go city traffic. i usually dont take it much higher than 70. before i changed the tie rod ends it would shake and vibrate too much above 60. but in ist current state i really wouldnt be afraid to take it up to 90, maybe more if its absolutly necessary. but i have put my maverick in the 100 mph club. as far as mpg's i get like 20 city and 30 hwy. the 2bbl upgrade really didnt hurt the mpgs since its progressive. just helps feed a higher rpm and it'll pick up harder if you want. as long as your water temp is good and you got good oil pressure you can keep going
Give the car the once over, Belts and hoses and check the tire pressure and roll on Highway, roll on along..... The Maverick in my avatar is a 1972 with the 200 I6 and I flew to Florida from Maryland and bought the car on a Sunday morning and drove it back to Maryland that Day and over 650 miles and a few hours time I was home. I cruised between 65 and 80 and ran up to about 85 on occasion getting out in front of traffic. I personal also drive that same car 53 mile round trip to and from work every day and I don't worry about it breaking down. A 302 withg the 3 speed manual and the 2.79:1 Rear should cruise at 80 with no problem. Not that I recommend you cruise at that speed and get yourself a ticket but I don't think she'll have a problem doing it..... Take your car on the trip to see your Grand Dad and show him what a nice car you are driving.
I drove my 77' from Boise, Idaho to Colorado Springs w/ no problems, then from there to Fort Lewis. My altenator fell apart, I say again FELL APART, cause it rattled the screws out, but she ran like a dream. Tighten everything every night and all is good.
I drove my 72 maverick from Memphis,Tn. to Commerce ,Ga. and back as well as all over town for Fast Ford weekend 70 on the interstate no troubles, was a good trip Jim