External oiling question

As far as need - it'a combination of things that determines whether or not it's needed. Going 8s in a slingshot doesn't take a ton of horsepower. They're light. I've got two teams I'm familiar with locally - one runs in the low 11s with a carbureted V6 Buick from the mid 70s - totally stock with 4bbl, a cam, and home made zoomie headers. The other runs mid 8s with a N/A/ small block Chevy and mechanical methanol injection. It makes about 500hp. So would a digger need it? Probably not unless they were really spinning it.
The suction side restriction is NOT the pickup ID. It's the passage between the pickup and the pump boss. Shine a light down there and you'll see why. The two passages intersect at about a 60° angle and the interior corner is a knife edge. Not good for fluid flow or flow redirection especially on a "pull through" scenario. That's where the additional external suction line comes into play. Because no matter what you do in the pick up boss - if the clearances are wide (as in high rpm expectation) or as referenced by the Hemi head comment the drainback is poor - the pump has to move a lot of oil and the bigger volume pumps can't suck hard enough. It will cavitate and put foamy oil into the bearings. Part of my standard big block oil system mods is to smooth out and round off the intersection point of the intake side above the boss. This was one of the mods addressed in a book I've had since 1986 - One of the HP books on Mopar Wedge V-8 engines. Seems like a lot of the books coming out now may mention the modifications but fail to note what the cause for it's re-engineering was. In this case it says it's a circle track/road race modification - but big blocks were starting to be regulated out of circle track at that point so I think the info started to be left out. The only other reason would be a larger stroke crank -anything beyond 4.25 (and some 4.15s) may need the external line(s) because the rotating assembly will not clear.

Edit - to the OP - whether it clears of not depends a lot on the Kframe and mounts your car has, and how the external line is plumbed. If it were me I'd mock it up without the line in the chassis, see what you can do, and then do it.