Re: 1970 Chevelle Base - 307 - 350 swap
The 350 will bolt right in place of the 307 but you may want to look for 350 frame stands. You can use the 307 stands but you'll have to transfer the block side motor mounts from the 307. Stock converter and flexplate will work fine.
I would look for an HEI distributor and headers.
The 350 you're building isn't going to set the world on fire but it will be lots of fun. Don't get hung up on what number it will make. That number may depress you but it's plenty to work with for now. The rest of the car isn't ready for a number that will make you proud and if you spend all your money on an engine you won't have any left to replace the weak links that you will undoubtedly find behind it.
69 Malibu Stock 307, Reverse Manual TH350, 4,500 Stall Edge Converter, 4.56 Spool 35 Spline 12 Bolt
76 C20 VortecPro 496 628HP 655 lb/ft TH400 Edge Converter, 4.10 14 bolt