you have 3 routes:
---3 point mounts *cheapest* ... theres 2 mounts that pivot and rotate, and then a bellhousing that clamps onto the pump itself for alignment. these are usually cheaper.

---typical mounts *good*. plate gets mounted to the front and rear gets small bellhousing that DOESNT mount to the pump. alignment and angle are all set by how the "feet" are bolted to the stringers.

---full plate & rail kit. *best option, most expensive. biggest pain to first install, looks bad ass*
3/8" plate mounted front and rear, pillow blocks bolt plates to rails. rails sandwich load across entire stringer.
(note image is a bbc not bbf but same shit)

keep an eye out for the sale section in this forum, riverdavesplace, performanceboats, and craiglist/ebay. deals are out there for mounts.