You will probably have to redrill the mounting holes so a Bosch 1617 with a fixed base ,remove the phenolic base and bolt it to the underside of the table. It is made for above table height adjustment. You might have to drill an additional hole in the table top to run the adjusting wrench through.
https://www.rockler.com/router-bit-height-adjustment-handle
Herb
https://www.rockler.com/router-bit-height-adjustment-handle
Herb