Re: 427 SBC or 496 BBC
I agree with Larger Dave. I went from a SBC to a BBC. What you have works and that is a huge plus right out of the gate. only thing you may want to look into upgrading is your radiator if your higher HP rating calls for it. Going BBC - you have no choice in the matter. Add to that a new pulley system, motor mounts, frame mounts, headers, manifold, carb, linkage, proper clutch bellcrank and linkage or hydraulic clutch set-up if going manual, bellhousing, starter, flywheel and dual disc clutch or flexplate, and driveshaft just off the top of my head. Parts add up quickly! And one last thing, you are already used to that high revving SBC, big blocks are all torque so it is a different feel and power. You will easily loose 1000 rpms on a built BBC from what you are already used to.
Although it was cheaper for me to build a stout 572 than a stout 427 - I lost on the other end where I had to literally replace everything including the trans and rear.
'68 Camaro with RS conversion
Moser 9" with 4:11
Martz Chassis 4-link and Front Sub-frame
Tremec T-56 Magnum 6 speed
572 BB - CM Engines
Wilwood 6 piston front and 4 piston rear disc