Hey Max,
Been closely watching your journey, most impressive! Please keep the videos coming
I don't have a direct radiator experience with 70 series. But I once replaced a radiator on an HDJ80 with an aftermarket aluminum with lasting success, dare say, improvements. But there were two caveats:
1. The 'cheap' aftermarket aluminum radiator was TIG reenforced and pressure tested prior to installation. Using an AC TIG and filler wire, I was able to 'reflow' and double the beads at all the strategic spots (tube-tanks, tanks-ports, tanks-mounts). I then ground up the beads and made everything look neat. A thin coat of radiator mat black finished it all.
2. Instead of more cores, I went with
less cores more passes. I know this might sound counterintuitive but hear me out: With more cores, coolant can flow from the upper tank to the lower tank faster, which means that the the outer extremes of the matrix (tubes further away from inlet) will potentially see less volume, reducing efficiency. Of course this is not always the case as this is highly dependent on the overall setup.
There are other disadvantages to more cores, such as the heat reabsorption by the rear cores, the reduced overall matrix cavity to factor in the wall diameter of the additional tubs (compared to an equal depth matrix with less cores), and the fact that the typical coolant flow rate would limit the time for coolant to shed its heat while vertically traversing the matrix.
Less-cores-more-passes radiators (think: dual core three pass) would permit better dwell time for the coolant, nearly eliminate reabsorption, and obtain a closer to ambient coolant temp at the outlet. Of course there are some disadvantages to this setup too, such as potential for the need to have a higher pump rate, a reduction in matrix structural integrity (at least compared to equal depth higher core number matrix) and, in the case of dual/quadruple passes: reversal of outlet side (triple pass don't have that problem, obviously).
Having the coolant traversing the matrix laterally in three passes can substantially increase its temp-drop efficiency as long as your flow rate can take advantage of this setup, in most applications, the OE pump rate is suitable for this setup.
On that HDJ80, I acquired a generic two core three pass radiator that roughly matched my needed size L,W,D (that unit was advertised as a Volvo diesel charge air cooler for a big truck IIRC).
Again more cores is not always better. I invited you to read more on this topic. Best of luck!
. It's difficult to judge the quality with it mounted as so much of it is covered up. It very much appears to be a near exact duplicate as I haven't noticed any modifications in how it was mounted. 
