The BC1's pictured (SPENDOR, my dear boy
) are later ones with the larger, foam damped and tuned port. The bass was very much better on these. The older ones had a smaller hole in the front baffle and when I got my BC2's sorted I placed a 12" square cushion inner in the top of the box behind the tweeters and put a couple of Maplin port-tubes in the holes. The bass, which was always better than early Bc1's is now even better and I don't get the "OOOM!!" which the older BC1 could give
HiFi Dave's suggestions are spot on and if the Harbeth versions are abything to go by, the Something Solid XF (?) model would be ideal in 35cm height. Mark Orr can make them exactly to size and supporting the box on four carbon pads at the cabinet extremes allows the panels to breathe better (certainly the lower one).
At their best, the midrange is what the BC1 can do so well. Tactile and natural, these speakers were designed to reproduce speech to a good standard and IMO they still do. Today though and for more percussive material, I'd probably suggest the SP1's which can still be got for £300 or so in reasonable nick - mid as good, smoother and far better bass handling - top is better integrated as well..
The HF1300 has a dreadfully narrow bandwidth by today's standards, only reaching 14Khz before the Coles super tweeter clumsily takes over and it has a nasty but well disguised resonance at 3.5Khz as well, but what it does in the frequencies it CAN reproduce is much better than most of the standard fabric or metal domes spitting away on most modern boxes IMO..
Enjoy the BC1's and try to use them as intended in open space. Don't overtighten all the screws as the panels need to breathe a little and crushing them together Linn style isn't the answer. They're a very easy load, so fancy mega-stranded wires aren't needed either. By the time of yours, Spendor had uprated the internal wires to a 32 strand as I recall - quite adequate for an 11 Ohm loading in such short internal lengths.
Lastly, the modern versions of this product (Spendor SP1/2r and Harbeth HL5 ES2) both sell for around £3,000 - makes you think.....