Hi Steve,
I recommend replacing the stock 2.8 valves for 2.9 V6 valves, but only if you intend on porting and polishing the heads. If you don't open up the ports all the way, the larger valves will not receive full benefit of full air flow.
You can run stock 2.9 valve stem heights, as the cam, although it will have near .500 lift, they will not interfere with the cam action.
I recommend using stock 2.9 V6 springs and retainers. They are good to 7,000 rpm, which is where I recommend redlining the little V6.
I recommend milling the heads a max of .030", because the extra 1/2 point will make a difference in performance, but will still be able to use regular gas. I think stock pistons are just fine, but if you want more compressing, I recommend not going over 9.5 to 1 compression. I always ran stock pistons in all the non power adder engines I built, but if you go with a power adder (blower, turbo, or nitrous), you'll need forged pistons.
You won't need to notch the pistons for valve clearance, since this is not an interference engine. I would still clay the valves to make sure you will have at least .100" clearance.
Either set of heads will work. If the Mutt II heads are from 1974, tthen they would be the preffered set.
I used to recommend a guy in Tacomc, WA., but he takes a long time to turn them around.
If you have anymore questions, please drop me an email and I'll be happy to answer them
I know this has been covered numerous times. Cylinder heads; I am starting to collect parts for my 2.8 build. Install Ford 2.9 valves or? What about installed heights for the high lift Jose cam, what springs and retainers? Mill the heads .030 to increase compression 1/2 point? Should I also send the Offenhauser manifold with the heads to have manifold milled also? Is there room for some type of positive oil seal on the valve guide top with the high lift cam? Pistons; buy the taller crown height piston from Summit? Is notching the pistons for valve clearance needed? I have two sets of heads, Mustang 11 and Ford Ranger. Probably use the Ranger short block with Mustang front. Either heads will work well? Recommendations for a shop that can the 2.8 head work (porting) This will be a good start, more questions to follow. Thank you in advance. Steve V. 2.8 In Arizona