Big Block Swap
To the OP.
Go for the big block and cross off the items on the list.
When i built my 67 dart i had a 440 block and a 340 block. I debated for awhile but i had the majority of the sb items i needed, plus the 340 was rebuilt. (20kms later it spun a rod bearing)
I stroked the 340 and running w5 heads now.
Hindsight i should of went 440.
Now i am collecting parts for a 400 stroker build for the 67 dart. So i have come full circle.