Well, I still advice him to try since things - no doubt about it - will change. But ride height may or may not be an issue, in this kind of suspension springs don't compress that much and height therefore isn't drastically affected by different rates. I wouldn't recommend going from well worn 140 springs to brand new 164 ones, though - wear imo affects ride height in a far worse way than stiffness.

Obviously I also should have mentioned in the first post but I've tried both setups in my 120, converted with 140/160 front suspension.

Martin
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'65 121, '73 165