I'd go with the Holley unit based solely on what I've read on-line.
Regarding upgrading the fuel system. Keeping and using a stock tank with an up-sized return line silver soldered into the stock sending unit is an easy alternative to buying or cutting up and installing an internal fuel pump in an aftermarket tank.
I plumbed my EFI this way. To do this, I run an external pusher pump mounted near the stock tank that feeds a Surge Tank mounted in the engine compartment that free flows at near "0" psi back into the stock tank through an up-sized return line.
Key point here, you have to have some sort of air free fuel supply to the pump. You cannot just hang an in tank pump on the end of the stock pickup in an otherwise stock tanks and have it work, BTDT.
Went I first did an EFI swap I found that out the hard way, stupid Holley said nothing about it, old analog Projection system. One burned out pump and a tow later I got busy.
I went the surge tank route, using the stock mechanical pump to feed it, with the EFI return also plumbed into it and a return to the gas tank from the surge tank. But I had to make all that, no one was making anything like that back then nor was there any help on the internet.
there are plenty of ways to address the issue, from the pay someone to do it route and the way to making and doing it all yourself. I fall int eh middle these days, I'll put it together using parts others make, generally minimizing my fab tome these days.
