How big of a dome?

68-396  how big of a dome can you run safely, before touching head or doing damage?  OH!! OPEN chambered 454-118cc heads.  

If you contact your piston manufacturer and tell them what head, bore, stroke, rod length, you have they can recommend a piston dome for what you have. That is what I used to do.  I would still do a valve clearance check before ever running the engine.
Just tell them what compression you want to run. If you are running street with pump gas and iron heads I would stick to a near stock ratio. With aluminum you can go a point or so higher.
With racing gas you can go 15, 16-1 but that stuff costs 8-14 dollars a gallon, and that was 8 years ago when I was racing, and would be for race only.  
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welcome and thanks for the update on your head style.you must tell us what your intensions are, so to start with a 118cc head and a flat top piston will avg. around 8.5 to 1 comp. can be run on reg. and can be a little bit fun. you changed heads so keeping it oem isn't an issue. check the block, bore it as large as safe, and put in a stroker crank. if you use the closed chamber piston I think they will fit but may have issues and comp. will be off by a point and a half due to the 10cc or so chamber size diff in heads.