IF there is meat to drill into the sides of the frame at the location where a specific set of angle brackets wind up positioning themselves once mounted to the cradle/crossmember, insulator mount, and the transmission, why not just drill new holes to mount the angle brackets(or weld them on) if receiving nuts can be fitted inside the sides of the frame?
Secondly, I believe the numbers stamped into the angle brackets can be converted into the Toyota part numbers for those pieces. I wrote those part numbers in the related thread elsewhere here. Example: "R-FB020" = 51433-60020 = 8/80 10/82 for the 40/42/43/46 series.
LITP has found the 2 variations of the long cradle/crossmembers to be the same length (which I find to be 20-15/16"/532mm).
There are 3 different insulator mounts that fit onto those cradles: different for the BJ4x, FJ4x, HJ4x. Apparently they all fit the cradle equally but have different thicknesses. So............the selection of which insulator mount chosen needs to be factored into the final position of the side angle brackets chosen to create the overall positioning of the transmission height. Along with the variations in the distance between the frame rails at the actual cradle mount location, this appears to be the reasoning behind the 6 slightly different sets of angle brackets designed by Toyota.
Along with the different tunnel inspection cover heights, different angle brackets, different insulator mounts, it seems that unless replacing a factory-installed five-speed with the same exact parts, adjustments need to be made when installing a five speed where there never was one originally. This is also complicated with the lack for most folks of the rare and hard-to-find 40 series top cover and the distance of the non-40 top cover to clear he inspection cover.
While on the surface the 4x series vehicles "look very similar," the differences start to add-up, and it seems a simple plug-and-play drop in installation doesn't exist for the five-speed conversion, and adjustments need to be made to fit each particular situation. Searching for the rare and unusual parts can kill the enthusiasm for a conversion, so it seems crafting the parts you have and can acquire to fit your own situation might be the best solution.
My thoughts only and not gospel. Value = 2 cents.