You must have a program somwere in ROM to load the programs in RAM. In ROM memory at the interrupt addresses (003h ...) you must som jmp instruction to RAM where you can write the new interrupt rutines (eg. jmp 8000).
The RAM memory must be selected with PSEN (if you want to execute instructions from here). Also the memory must be selected with RD and WR signals, for read and write operations.
When you compile and link the programs, the code must start in in the RAM (eg. l51 xxx.obj CODE 8000h).
After the ROM program load the program in RAM this must maje a jmt in the RAM address where you store the program (if the RAM can be selected with PSEN the program will run normal)

PS: you can mail to me for other suggestions. I have something like that where I test the programs before write the EPROMS.