The '70 would be a better GL in my opinion also. The main thing is, the '70 has an IRS rear suspension already. So, it will handle curves like most GL cars are, curve carving speed freaks.
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1970 T1 W/MassIVe 2913cc RAT/?EFI? w/direct fire (very soon) and 915 trans
1962 SC 1776cc SP 944NA brakes, 993 wheels
VKG