Maybe re-ring it and run a hone thru it just to clean it up for a sec. Maybe check the bearing. If you trust the engine do nothing and just replace the cam with a mild HYD flat tapet cam. something the the RPM cam. bolt it together drop it in. Thats the cheapest way i can thing of right now. Your going to need some pully bracket's also. I like the March set up.
I use brackets from a 1990 Lincoln Mark vii on my Engine. Any 302 brackets will work (some with minor modification). If you're yanking your 302 out then you can use all the brackets you already have on the 302. You can and should use the Timing cover and water pump off your 302 if they are different from whats on the 351. Use a a Distributor from a Pre 94 351 EFI truck. Its the one with the Module on it. (looks just like the one from your 302 but the shaft is thicker to accept the larger oil drive shaft)
If you can use the Balancer and flywheel from the 351. Your 351 is External Balanced and has a different balance than the 302 so keep the flywheel and balancer from the 351. If not make sure the new one has the same balance. (I believe its 28oz for the 351) Also stay away from CAT performance parts here.
Swap Headers will work fine at this point. The heads that you have aren't so radical at this point.
As far as the Lower intake...are you Going EFI or carb??? If you stay EFI its basically Plug n' Play. Carb is a little more work changing things a bit. (If you go Carb forget what i said about the distributor and get one with a vacuum advance)