Press-in bottom bracket bearing are not very common for bikes. If you cannot find a high end LBS that can do it, I would suggest taking it to an automotive machine shop, see if they can (carefully) install it with a hydraulic press.

Most Merlins would have been sold by the framebuilder as bare frames to be built up however the distributer, LBS or final buyer wanted it. I wouldnt get too hung up with trying to replicate components for a particular "model". If you just build it up with period correct selection of interesting high end components, that will be much more representative of how majority of Merlins were originally sold. Alternatly, find some pictures or specs for a sponsored team bike and replicate that build. Lance Armstrog was riding a Merlin while he was on subaru-montgomery in early 90s, shortly before he turned pro with motorola, that could serve as a good representative build spec.