Dude an almost stock 400 would handle what you have going on.....if it were an early 70's or older core that came stock with torrington bearings. I've built 3-4 400's in my time that were all stock rebuilds, all for cars running 8.00 or better in the 8th, and none of them broke. The good thing about a 400 is they're about $150 of craigslist and the parts are cheap. I had an all roller bearing furnace brazed 1/4" anti-balloon plate 3400-3600 converter in the Chevelle that was only $650 new.