Dean, I can relate to the gettin old bit.
Firstly what I'm about to say is just me relating my thoughts. I don't want those who are running the 5Ltr taking offence at what is said.
Dean, the 5Ltr with it's bluddy ugly intake manifold just does not do it for me. Given that you already have the 351 and obviously want some benefits of EFI then have a look here:
http://www.mass-floefi.com/mass-flo.html
A system like this gives you all the ole traditional cobra charm of a carby set up but with the advantages of EFI. It uses a reprogramed ford ECM which saves you buying a Motec or Autronic or similar.
You can use whatever cam you want together with whatever heads you want so you can go mild to wild.
I'll send a PM with a number to contact me.
Cheers