Like me, ordering direct from Serpent USA is the WORST thing to do.....ordered 15 items, send 4 items in 3 shipment, the rest.....la la land.
Yes, buy the small block engine mount then you will have tons of engine to choose from....
From my experience....BB 15 does easier to tune, last longer, runs cooler.....however, BIG BLOCK 15 does not necessary any powerfully then small block 12/15 like back 4-5 years ago when small block 12 is just released. Engine like Nova MAX 15 or JP mod 15 or MEGA 15 (even stock) are par or even faster then CX15 or X15 big block............but you have to pay the price, and these small block DOES WEAR FASTER , way faster the big block engine....talk about 1-1.5 gallon of fuel, you are ready for the whole engine internal replacement compare to easy 2 gallon for BB 15.
I would definitely buy the $30 engine mount and take advantage of the latest SB 15 technology.......
I do not see Ashford has X15 BB listed, but you can give Robert a call, I don't think it is less then $300....
On the other hand, MEGA SB 15 (by Serpent) is less then $210, combo is around $260....I think that is a bargain.