Fitting a Flex Plate

[MacQuigley]

Im going to be putting a 454 into my truck fairly soon but its the engine coming out my dad's Cobra and as he has a manual box and Im going auto I need a flexplate.

Ive never bought one before and Im keen to know if there is anything that I need to look out for. For example I read that on a 454 the flexplate should be paired with the harmonic balancer because its externally balanced. Is that correct and is it easy enough to get a supplier to supply the parts as a pair.

Equally what do I need to look out for in a torque converter?

All very new to me as Ive always run manual transmission in the past. There is loads of info out there on what you can do, Im just unsure as to what I should do!