After spending a lot of time and money fiddling around with Crane 1.5 Irons, 1.6 Irons, then regular 1.6 Harland Sharps on my 383/451's Stealth Heads, I found that the 1.6 Harland Sharps for Edelbrock heads (S70016KE) were the only ones that gave me correct valve tip geometry without any special shaft adapters, shims, or other high dollar geometry "fixes".. Once that was set, I ordered a set of Mantons at correct length and I was good to go. Nice narrow tip pattern in middle of valve stem with about .560 net lift. Also increased pushrod clearance a ton when compared to Irons. Shanon's hooked me up. They're not cheap but I wasted 2x the time and money screwing around with the other setups.