If the thrust is within limits with the old existing bearings then I'd use them if they are the older lead/copper type, rather than the newer all metal ones, I have just done so, after 200K miles mine were within new limits.
How good is the old oil pump ?, chances are it will have some wear look particularly on the lobe edges as well as end plate grooving + scoring.
Good chance it will have wear in which case a new one should be sued.
As you know there are some dodgy genuine cosworth ones around, and some that are mentally high pressure, 60 psi is more than adequate, as in a standard pinto oil pump, this again is what I have used, £24 new.
Be aware there are many very bad quality oil pumps around, a lot made in china that are crap some even machined without the hex drive hole!!, still even they are busting apart like the cosworth made ones.
The place I use are rejecting around 50% of the pumps they are sent, each one is inspected and these are what they use on their own supplied and warranted engines.
The HG will be fine at 400bhp, and will cope far better than a metal one if the surfaces of the head or block are not perfect, due to it's fibrous nature, std head bolts will be fine, as would arp so long as depth checked(arp).
tabetha