Custom sizing query/worry

you're 6'2" and riding 55cm? ?

standover height 82.5cm - i.e. it's more like a 58cm

You made the bed (hopefully without completely ignoring the advice of a well respected frame builder).
If you're not going to lie in it, who else will.

the frame builder (jeff), was fully supportive of what i was asking, i said from the outset that the ideas of how i wanted the frame to be built were simply that; ideas.
he agreed that the bb height was high but said that it was totally doable, he set the jig up according the bb height and the head tube angle - therfore getting a seat tube of 55, on the basis of that the top tube was set to 54 (which seemed comfortable)...