I actually went to this shop to only buy some RG-8/213 to rewire my mobile...never expected to walk out with an amp!
Another question I have is that since this amp lacks a remote, can I parallel three or four ice cube relays together (assuming 30A per cube, 4 would provide around 120As worth of switching), and simply turn switch the power on/off to the amp? Will that cause any issues, such as spikes/surges?
No need for relays, just run your pos/neg power leads.
All a remote switch does is to add 12 volts to the keying terminals of the relay inside the amp to switch the amp from receive to transmit so just find the pos/neg legs of the relay and attach wires there and add a (stereo) phono jack in the back of the cabinet and then wire a toggle switch to a stereo input plug making sure to put the positive lead on the tip of the plug and the negative lead to the center lead of the plug and jack.
The guy you bought it from should be able to install this for you if he's worth his weight in salt.