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The .474/.510 lift of the ZZ4 camshaft is already too much for the heads/valve-springs in their stock configuration, as somewhere around .470 is about it (the retainers will hit the valve-guides/seals). You have a couple of choices that will let you be able to run a larger cam in your engine, such as pulling the heads and having the valve-guides cut down and installing appropriate valve-springs or to install a set of beehive springs such as the Comp 915’s with the matching retainers and locks to allow them to be used with the 11/32” valve-stems of the SBC vs the 8mm pieces of the LS style engines. Regardless, if your planning on adding 1.6 rockers or another camshaft with lift in that range, I would recommend going ahead and pulling the heads to have them properly prepared for the camshaft your planning on using and due to their age, they probably need freshening up anyway.
I wouldn't waste my time on the ZZ4 cam. If you are looking at a cam from GM go with the LT4 hot cam. It will get you into the power range you are wanting, has a subtle lope to it at idle depending on what speed you idle it at, makes decent vacuum (15 inches at idle) on my old worn out junk and has some wicked mid range torque for what it is. Some will tell you there won't be anything on the bottom end but I lug the thing around town as low as 900 rpms in OD with the converter locked and it doesn't even bat an eye. It happily hums along like its nothing and will easily jump to the speed just easing into the throttle. I am using 906 casting vortec heads that I ported, the guides were redone, they got a 3 angle valve job and new seats, and I am using PAC 1218 springs, I don't recall the comp retainer number without looking, and LT4 valve locks which I'm pretty positive are the same as stock valve locks. I was going to use the thinner comp locks that place the retainer up another .050 higher on the valve stem but I found one cracked right out of the package and another cracked when I was installing them. I threw that crap in the trash and put the LT4 locks back in place.
1995 Chevy ECSB, currently dead at 207,230 miles but is getting a turbo'd Little M 400 small block
99 NBS Silverado Z71 - transgo HD2, 3 inch dynomax ultra flow, 05+ efans, tuned with Efi Live, Ford keys and 305/70-16 Mickey ATZs
The only problem you are going to run into is a lack of fuel injector. I had a tweaked SBC vortec I installed in my monte. I used the Hot Cam and a set of Stock heads from scoggin dickey that were worked over to let you install larger valve springs.
The motor ran absolutely awesome for what it was but was dangerously lean on the top end even with the injector duty cycle maxed out. I never had any problems with the combo and it was a real nice street package.