You first need to decide on what HP range you will likely fall into. The stock siamese head is capable of supporting HP levels over 600 HP in naturally aspirated trim. The car shown in my avatar is one of such an example. The Kirby/Sissel aluminum head is a good upgrade, but very expensive and availability is limited, and maybe no longer able to obtain for much longer according to Kirby. By the time you get all the parts to make this conversion complete, you will spend between $5K-$6K. Speaking to Kirby several weeks ago, he is machining another batch of heads now, and only has a few extra that are not already pre-sold, after this batch he probably won't cast anymore, he says his patterns are in terrible shape and it just isn't cost effective to invest the thousands of dollars to repair or replace them. We upgraded his intake port for this head for him in 1992, and counting this batch of heads he is working on now, he has only sent (25) out the door in 17 years, so you can see that the expense to put back into the patterns will hardly be cost effective for him, since the return just isn't there from a business stand point. The Frankenstein style head that Leo did isn't really an option, because the work and labor required to both the block and head(s),just doesn't yeild the gains you can achieve with a siamese or Kirby/Sissel head. I was talking to Leo recently about this mod he did with the SBC heads, and asked him why he chose to use this method, since he had the ability to use a much better head for his project. He said he just felt it reflected the extreme limit of what could be done with these engines, but also said that it suited his needs fine. There is also another cylinder head option available. Although, it is often difficult to obtain, and that is the Brazilian 12 port head. As the name impiles, it has 12 ports(6 intakes and 6 exhaust), but is the same in everything else as a regular siamese head without being siamesed. Several guys on here have used them with great results with turbo set-ups, but again, they can be hard to acquire at times, since they have to be imported from Brazil. I think the best "bang for the buck" for you will be the stock siamese head, as it can support HP levels from mild to wild with doing very little to them.
