ERF9530 is a rebranded TO-3P MOSFET, similar in size to the power regulator on the side wall of a Galaxy or other similar radio. It will probably be too big to fit in place of an RM3 transistor.
IRF9530 is a TO-220P (final sized) MOSFET, has lesser heat dissipation then the above.
By doing a deep dive on the web, a German company web page says RM3 is about the same as an MS1307.
https://www.mwf-service.com/shop/mos-rm3-hf-endstufen-mosfet-max-30-mhz.html
Another site says MS1307 is equivalent to an IRF530 or BUZ20.
http://www.datasheetcafe.com/ms1307-datasheet-mosfet/
Going on the International Rectifier web site, their PDF listings for IRF510-IRF540 show
http://www.irf.com/product-info/datasheets/data/irf530.pdf
IRF510 - Id - 5.6A - Ciss - 180 pF (used in some experimental QRP ham transceivers)
IRF520 - Id - 9.2A - Ciss - 360 pF
IRF530 - Id - 14A - Ciss - 670 pF
IRF540 - Id - 28A - Ciss - 1700 pF
Id is Drain Current, Ciss is Input (Gate) Capacitance.
IRF9530 is a TO-220P (final sized) MOSFET, has lesser heat dissipation then the above.
By doing a deep dive on the web, a German company web page says RM3 is about the same as an MS1307.
https://www.mwf-service.com/shop/mos-rm3-hf-endstufen-mosfet-max-30-mhz.html
Another site says MS1307 is equivalent to an IRF530 or BUZ20.
http://www.datasheetcafe.com/ms1307-datasheet-mosfet/
Going on the International Rectifier web site, their PDF listings for IRF510-IRF540 show
http://www.irf.com/product-info/datasheets/data/irf530.pdf
IRF510 - Id - 5.6A - Ciss - 180 pF (used in some experimental QRP ham transceivers)
IRF520 - Id - 9.2A - Ciss - 360 pF
IRF530 - Id - 14A - Ciss - 670 pF
IRF540 - Id - 28A - Ciss - 1700 pF
Id is Drain Current, Ciss is Input (Gate) Capacitance.