Weld-in frame connectors do help alot, and with solid body mounts, you're transferring the shock to the body verses having the bushings absorb the shock.
I don't remember the P/N to mine, but they are CE and they are mandrel bent to clear the floor pan in the rear. Yes, they do hang down, but I painted them black and you don't notice them.
You would probably want the type that goes through the rear floor and the floor is welded to it for added strength, especially with Konis and Hotchkis, you want the lower center of gravity.
If I were you, I'd replace the solid bushings at the radiator support with the stock bushings. This would give a cushion for the radiator, they hate vibration, that is, if its still mounted like OE with the soldered panels on the side of the tanks and bolted to the radiator support. If you've engineered in a set of radiator mounting items similiar to late model, rubber bushings clamped top and bottom on the seams, that's fine. Leave the solid bushings in the support brackets.
Well, you've got the solid bushings, the frame connectors, might as well install a good 8-pt roll bar, it would really tightened up the car. Just be sure to have the frame structure checked for straightness first, befire doing the welding of f/conn, and roll bar. If not, and the car is crooked, it will always be crooked. Just be sure to have the car thrust angle aligned when done, it'll work wonders.
But then, how would one do this in Europe? I can imagine the language barrier.
Well, I've rattled enough here, I'm sure others here will have some good suggestions also,