It would make sense to hot tank the block and freshen up the bottom end (new main bearings and what not). You are only as strong as your weakest link and I would predict eventual trouble by having a brand new top half of the engine and an original 40 year old bottom half. Hell, while you are at it, get new pistons in there. the rods can be reused. Like the previous poster said, plan on this as a project. Create a spread sheet of your actual and anticipated costs. You can save a lot of money if you do what you can by yourself. I think you can install the intake and heads yourself. Pay a machine shop to hot tank the block, shot peen the rods, install new pistons and rings, shot peen and re-grind the crank, rebalance the crank, and install new main bearings/caps, . Get your short block back and install the heads, intake, and carb yourself. It will be fun.
On the other hand, if your plan indicates that from start to finish your costs will exceed $3000, then just abandon it and get a new crate engine. Ford Racing has a 302 roller block putting out 345 hp and which costs around $3500. It comes with a 12 month/12,000 mile warranty.
Here's another optionone that I did a couple years ago) You can buy rebuilt roller shortblocks for less than $1000. I bought one locally for $350 (exchanged, meaning you need a good core shortblock needing a rebuild to trade) I ordered a set of ARP rod bolts($45), installed them in the rods without disassembling the engine (and they say you can't ) Swapped the cam for a B303 hyd roller from Ford(used $100), changed the timing set to a double row roller chain($45), Ported a set of E7TE heads myself(total for the heads was about$150) bought new pushrods, a set of used 1.7 "Cobra" roller rockers($125), a new but second hand Ford A321 intake ($150), a used Holley 650 DP (rebuild kit and new base plate was $150). The shortblock was built by City Motor Supply in Dallas Tx. and came with 40 over Silvolite Hypereutectic flat topped pistons. I ran this motor in my 89 Ranger for a year and a half, with daily "freeway blasts" up to 6500 rpms, then swapped on a set of Canfield heads & a Vic Jr intake. With the this top end, I ran it another 4 months with daily trips to 7500 rpms. In the end it cracked a cylinder wall. I limped it back home and pulled it then. The stock bottom end held up fine. The pistons and rods were sold to another guy who's got em in another motor. Bottom line is you don't have to spend the bank to build a good lively street motor, that build up cost me about $1500 total with gaskets and it probably would have lasted longer had I not subjected it to the abuse I did. Another option is to find a good "donor car" for a roller 5.0 and swap the engine into your Stang. Good used Lincoln Mark VII's can be had for $1000 with the HO 5.0, and you can also pickup roller 5.0's in any 87-91 Crown Vic, Marquis, 92-97 F & E150's too (these are the same motor as the HO, but minus the forged pistons and HO cam) The 94 E & F150's actually have a good street cam , just a tad less than the HO's. The others have the smaller base roller. Both these options will cost you much less than what the others have suggested. And if you really want to save money, you need to do the labor yourself, shop time will kill you. If you don't know how, go out and make friends with the local gear heads, they'll teach you.