Here's a bit more info I found on the BB - C4 swap that I thought might be of help.
"if you put a bbc with aluminum heads, intake and water pump in , in place of the standard iron small block you only gain about 50-70 lbs, not enough differance to cause any problems at all, , I have worked on several of these swaps now and Im in the process of getting ready to do another one,heres whats needed
steering rack mounts cut and rewelded 3/4"-1" farther forward (that of course means the power steering pump lines/steering shaft, need to be extended 3/4" also)
small notch (starting at rear and going 3" forward from rear edge X 3/4"deep X 5" wide works well in rear top surface of (K) frame cross member to clear damper and pulley)(if you use an internally ballanced big block with the 6.75" dia. damper you can most likely skip the notch but with the 8" dia damper its necessary, and some oil pans will also require the back 1 1/2 of the (K) frame to be notched at an angle slopeing to the rear to clear them so youll probablly need the notch of some kind anyway)(and yes before you ask you could shim/modify the motor mounts up to get the clearance, but that would slightly raise the weight center and slightly effect the handleing, and that also makes the windshield motor and distributor clearance a bigger problem, a 1985 blazer wiper motor can be modified for greater clearance on the valve cover and swapped in to gain valve cover clearance)
air conditioner shrouding fiber glass on pass side foot well around the air conditioning on the firewall needs to be modifyed for clearance, (the fiber glass cover from a LT5 makes this easy)(evaporator houseing cover)
1971 bbc vette exhaust manifolds (or custom headers) and all brakets/pulleys (mods needed here)
(see the post on building your own headers)
oil pan needs to be only 7.5" deep max
3" hood scoop unless you run a low rise intake and carb or a low height efi system
for a step by step instructions with pictures get a copy of the august 1998 vette magizine article( starts on page 34)it helped quite a bit the first time
otherwise its almost a drop in deal, but keep in mind that youll need a bigger radiator, the trans will not last to long with that amount of torque and it may not pass emission testing and a small size starter is needed, and your windshield wiper motor needs to be replaced with a much smaller one,(I don,t remember where we got them but alittle measureing and a trip to the salvage yard took care of that problem, and no tall valve covers don,t work well!
btw install the short block then add the heads with it in the car its FAR EASIER THAT WAY than trying to install the long block
BTW the earlier cars like the 1984-86 (Im not sure what years exactly)dont have the heavier forward frame braceing above the stearing rack that makes this swap more difficult to do! I have worked on this swap on the 84, 85, and 86 cars so I know they work fine, the later cars like the 1992 with the heivier forward frame braces above the stearing rack look like they will be more dificult but still do-able with some extra work, btw theres a guy at ARIZONA SPEED AND MARINE that has one you might want to talk to .just a few points
an all aluminum bbc WEIGHS LESS THAN AN IRON SMALL BLOCK so the HANDLING IMPROVES
an aluminum head, intake and water pump bring a bbc engines weight to within 70 lbs of the stock iron small block, so handling is almost unchanged
any un-supercharged small block not useing nitrous or some other power adder that makes over 550 hp is highly likely to be at least somewhat unstreetable as a daily driver and your not likely to build a small block that makes "764 HP & 695 lb/ft at the flywheel" likely costs as much or more than a big block makeing similar power, look, good engine choice"
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