If you come up fairly close to those parameters, this spring right here should be close to 105 pounds seat with proper retainer and locator/cup selection. You'll lose between 5 to 10 pounds of pressure during break in. When I've talked to Ken about magnum or LA spring pressure, he said that close to stock pressures worked well, but I hadn't asked him about the 270 XR grind (I am about to get one ground, ironically enough, so I'll find out about open pressures for definite...), but the profiles I had asked him about were in the same neighborhood of lift rates.
HERS084 1.437 OD, 110/1.750 FT/HR Single Valve Springs
