This is the place who make the Ultraflow manifolds.  I've been meaning to post this for some time.  http://www.matildafoundry.com.au/index.htm
Here's the version for the alloy headed crossflow - reminds me of the Argentinian products! http://www.matildafoundry.com.au/mfadd2.htm
The GM manifolds they are offering are extremely well regarded, and priced fairly, from what I am told. One chap who knows his sixes pretty well opined that the best results from a N/A 250 engine would probably be had with triple Webers or D'Os but failing that level of budget, one of these suckers with a 500 Holley on top. Still not as cool as triples. 
 
More food for thought!
Regards, Adam.
				
			Here's the version for the alloy headed crossflow - reminds me of the Argentinian products! http://www.matildafoundry.com.au/mfadd2.htm
The GM manifolds they are offering are extremely well regarded, and priced fairly, from what I am told. One chap who knows his sixes pretty well opined that the best results from a N/A 250 engine would probably be had with triple Webers or D'Os but failing that level of budget, one of these suckers with a 500 Holley on top. Still not as cool as triples.
 
 More food for thought!
Regards, Adam.
 
	 
 
		 
 
		