If you already have an 8 inch rear you might keep it with a V8 swap maybe only changing axles/drums over to the 5 lug versions but if your car is a very early 1970 (key under dash - not in ignition) it would have the really small rear in it that uses a bolt on rear cover which I would say exchange it for an 8 inch
Welcome, and good luck on your project. My 2 cents.....do a lot of research and get a good understanding of all the parts you will need. Buying a rusted or smashed car that has the drive train you want will save money over buying everything by the each. First, decide what you want.....and give it much thought. There is a TON of Maverick/Comet info in this site, and most searches you make on the subject bring you back here. Learn to use the search feature here, and get used to this forum. It is full of great peeps, and will be your biggest help. Hope you like to read a lot.
Do you believe your grandfather's car would be drivable with just the installation of the engine and transmission? Do you have all the other parts i.e. radiator? From the single picture the interior looks a bit rough. That is fine as long as you do not have major rust issues. You did not address my question concerning rust. It is best to get the car up and running assuming there is minimal rust, otherwise you could be faced with a large investment and a non functioning automobile.
"a sentimental thing" always cost more than the return...how far are you willing to go time and budget wise? if you do the work yourself...no drive train, rust repair, paint and interior...a min. 12-$15 K and 5-7 years... JMO
