I’d look into something fairly efficient, since the 450 is only 15 watts per channel. A lot of small cheap bookshelves are pretty power hungry (mid-80s efficiency), and will sound kinda ehhh with a low-powered amp, and cause it to clip and distort easily when turned up. That can actually wind up hurting your speakers more than if you hooked them into some monster amp and fed them too much power. Klipsch speakers are probably your best bet, since they’re pretty efficient and sound quite nice on old receivers.

Found a used pair of R15’s for $109 on Amazon. At 94dB/1 watt, that SX450 will be all the amp you’ll ever need.

https://www.amazon.com/dp/B00LMF41IY/ref=cm_sw_r_cp_api_i_B1hSEb5T8156M