You can not run a solid flat tappet on a hydraulic flat tappet cam grind.
You may be able to run a solid roller tappet on a hydraulic roller cam grind. It all depends on what ramp rate was ground onto the hydraulic roller cam.
This has been done successfully by many people including myself.
Unless you are real cam guru I would first contact the company that ground the cam to see if it is feasible.
There are many threads here on FABO regarding hyd lifter issues, do a forum search to get the current do's and dont's be prepared to spent some time on this before you make a choice.
Good Luck
