Since I am not too familiar with the sound of the Heartbreaker, thought the G12H75 would be a good fit. If you want ALNICO I would consider Scumback as they make some good vintage style speakers, and some with ALNICO. Just do not get the PVC (paper voice coil) as that has a very low watt rating. You can order the Scumback SC75 in a 30W, 65W or 100W rating. I had considered the Scumback but went a different route with my Mark V.
The G12H75 Creamback is perfect for an EL34 based amp. I have channeled the Mark V though the RA100 Combo and it sounded good. I was not too impressed with them and the Roadster. I have also done the converse, channeled the RA100 to the Jensen and it made the clean channel pristine. It was not too shabby with the Hi/Lo gain channel. Still, my preference for the EL34 and overall tone of the RA100 goes to the V30 (closed cab) or G12H75 (open cab). I have also run both from the RA100 (pair of G12H75) and the Jensen, sounded great but still not the same. Not sure how a Jensen would mix with a V30.