is this a simple bolt in swap (crossmember, driveshaft, etc.)? i don't know if any of the parts are the same. it's in a '70. also, how much hp is lost through the 400 compared to the 350? faster times with a strong th-350??? thanks, greg

No it is not a simple bolt in swap. crossmember, yoke, and possibly driveshaft are different.

Not worth the trouble for a mild racer.
Only if you are looking for the last .005 ET.

You can net more ET change with a proper tuning than this swap.

Either is a good trans.

HP different is fairly negligable.
Probabyl better expressed as a percentage, TH350 about 10%. TH400 about 13%.

Good luck