[drunken monkey]

which is the better solution is also in part down to you.

As is pointed out, the Heller/Union kits offer a convenientt all in one, ready to build option for a decently detailed build BUT are an old kit and as such, is never going to be as sharp in terms of detail, as a newer kit.
There is also the simple point that the detail in these older kits may not actually be that spot on and if you are intending to detail it, will require work done to it anyway.

If you're willing to work on improving the details of the older kit, then that kinda suggests you should be equally willing to put work into modifying a modern (i.e fujimi) kit into accepting a HRM engine kits which will, despite being more work, will net you better results.

As for the kits, they vary in quality.
The Ferrari ones are really quite good and are probably the best of the lot.
The 917 is good but details are a bit soft and not as sharp as they could be.
The Lotus is nice to have in 1/24 but the engine is.... basic and there isn't any other 1/24 DFV that I can think of to scavange from.
Not sure about the rest as I've never seen them.

I do have a feeling that the Bently Blower maybe a re-issue of the very old Frog kit which I do have and again, it aint bad for its age.

If I were to build one, I would go for the modern kit+transkit approach.