Hi,
I'm an HVAC contractor and I have a job that has roof top units that are fed by two circuits; one for the heat pump compressor & fan, and a seperate circuit for the electric resistance heater. The unit I am replacing it with has a single point connection. I cannot get back to the panel. Can I run both circuits into a disconnect and come out of that into the RTU with a single feed? Thanks.

No

I think it's best if you contact a license electrician.

It sounds like you don't have a unit that will work with the existing wiring. Call the manufacturer and see if they have a kit designed for that unit that will split the loads.