23 or 18 spline?

OK , this has probably been done to death but I'm confused and maybe someone can help me. I already emailed Dan at Brewers but I'd like to get my fellow A bodies peeps thoughts. I have a 67 dart , weighs about 3200 lbs. 340 .030 over , 10:5/1 525 solid flat cam , Eddy aluminum heads , 1.6 RR , victor intake , 750 brawler carb. Hooker s comps , 23 spline 833 with a RAM paddle clutch disc and a Dana 60 with 4.56s. I would assume it makes 425HP? I exploded my 833 on the street but had a few people in the car power shifting and it was an older tranny. I have an untouched stock one in there right now but want to build my old one and have it be strong enough. My question is , will the 23 spline built from Brewers products be strong enough for street driving occasional power shifting and give me piece of mind or should I switch to an 18 spline? I plan on porting my heads and intake to get more power down the road. Any input helps. Thank you in advance.