I have a problem with my Holley 600 (4160)

These work amazingly well and they aren't that thick. Also you might consider pulling that intake and blocking those heat cross overs too.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=EDL-9265&N=700+115&autoview=sku

or if you want a center divider type:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=EDL-9266&N=700+115&autoview=sku