Just finished the interior Saturday night, so was practicing this very procedure. When I sat in a Superformance at Laguna Seca, they said, put right foot in, grab seat back with right hand, lean against seat about 2/3 way up, and pull left foot up and in, slide down. Getting out is more difficult, but basically reverse, pick self up so leaning against seat, left leg out, twist left, right foot out, let go of whatever you grabbed. Do not grab or use the windshield for any of it.
I think the forward roll bar support in the 289 is going to help make this easier for the 289 folks.
The cool cars are in the old guys hands because: 1) we can finally afford it, 2) many actually have the knowledge and fundamental skill sets to build and maintain them.
However, it is refreshing to see the younger folks jump into these builds, because that is how you gain knowledge and skillsets! Us old guys were there once!