At what point should I consider up grading to a stronger bell housing? Is it the RPM or the torque that can cause an explosive malfunction of the clutch / pressure plate assy? Currently building a 512 w/ approx. 600 HP. Now a stock bell housing and 23 spline 833.

IMO any time you are going to beat on a stick car you need a blow-proof bellhousing. If you are going to have stick tires it is mandatory. I have seen quite a few cracked cast iron bellhousings removed from street cars with sticky tires and "spirited" driving techniques. A couple of them broke the block as well. Like so many other items on a good car it is cheap insurance.

ASAP!

Thanks. Didn't think about the potential block damage.

Also buy a Billet flywheel , 40yr old, heat cracked, cast wheels belong on trailer poodles .

Also I'd upgrade to an 18 spline Hemi trans. I've seen 23 spline input shafts with the splines realigned by the clutch plate.