I always liked this idea, since I have never raced an automatic car in my fleet. About the pilot bushing or bearing, I think that it would fit in the crank, since it fits behind the knub on the torque converter, as long as the cranks for those engines has the clearance (I will look later). All of the parts are avalible from
www.thepartsplaceinc.com. They don't make a kit per say, but the parts can be ordered seperately to make the conversion. Pedals, bell crank, rods, and frame bracket. And the block has to have the boss for the ball pivot, as long as it is there, it's easy to drill and tap. Basicaly, it's in the Chevelle, Malibu, SS book. My brother and I did this to his 1983 Malibu Wagon, which was a G-body. He had a 400 SBC though. You will need a B O P or universal GM scattershield, and block plate, and the correct flywheel, that would have to be SFI approved, and has to match the clutch (11 or 10.5 inch) and they are externally balanced (like a 400 SBC and most GM engines after 1985). It also has to work with the starter (153 or 168 tooth). The clutch (I use Centerforce Dual Friction) has to match the input shaft of the transmission (10 or 26 spline). Would be real nice in front of a Doug Nash 5 speed.
About loosing boost during the shift, I took out a Subaru WRX, and I think that it was just fine, during the power shift, on the street. They rev to 7000 rpm (2.0L boxer), and I don't think that the 3.8 will rev that high without some damage. It's always harder to short shift at the track, at least for me, when the engine doesn't spin past 5500 rpm.
I am going to try a manual trans behind my other 3.8 turbo engine, when I find the right car and truck. I don't think it will be a G-body though.
About the thrust from the clutch, I don't think that it would be an issue, since some Toyota guys run the Buick 3.8 and a manual trans. Also, 1978 Regals had a 3 speed trans standard with the 3.8, and the turbo 3.8's were the strongest built of the even and odd fire 3.8 engines.