I already had them on my 351w and I had them cnc ported for my 408, even if I was buying new 205cc heads I would still go with the TW, the trick flow design is superior, even with smaller valves the trick flow makes a smidge more power, if was going a larger head I would run the TW-R even over the afr 225, the trick flow heads make the most hp per dollar than any head, a few years back afr was planning a rotated valve head but TFS still holds the patent. Other than a cleve style canted valve head you cant get much better. The twisted wedge design has way more flow at low and mid lift than other heads even bigger ones, so even with a smaller valve and port the intake cross section area is like a bigger head as the valve is closer to the intake mani.
it really depends on the cam, I ran stock style pistons on my 351 and a hyd roller with 542 lift but mild duration and I had tons of clearance, my new 408 has the probe pistons that have the dual reliefs for inline and tW, actually the TW have more valve clearance than an inline head with 202 valves. Usually anything over 224 @ 0.50 duration should have the relifs.