When my heads were first set up, the stock guides were too loose and in the morning it puffed. On the second go around, instead of knurling the guides, the machinst installed liners. This brought the clearances to within spec. The SI exhaust valve does not have provisions for a seal and I ask that they be left off. On the first valve job, it puffed after 1000 miles. I just learned to live with it. There is 3000 on this recent rebuild and it's not puffing and I expect it won't as long as I keep the maintenance up (which has never been an issue). The other issue you may need to be concerned with is retainer clearance. How will the installation of a valve seal (that wasn't installed by the factory) affect the clearance between the spring retainer and seal? Researching, I looked at Ferrea, SI and Manley valves. The Ferrea and SI valve stem length were close to each other, but the Manley valve was much longer. I would have had to use the Manley valve to obtain the the proper retainer clearance for the vavle seal. But I also wondered, at what expense to the valve train geometry. How much more would I have to change to get back to the proper geometry. As it sits right now, there is a 3 angle valve job, with 2 angles on the face of the valve. I used a combination of 0.050 plus retainers and keepers to keep installed height within 0.002 and stem heights within 0.002. You could lay a straightedge across the stems and not see any light. There are three 0.015 spring shims spread across both heads. Before each seat was ground, the stones were dressed. Kind of extreme, but I got a great valve job.