Pleasure - the important thing is to have fun.

The 8x54 should be within 1 gr. capacity as the 8x57. This is why the 6.5x55 was developed. The Swedes wanted a 6.5mm round that would easily fit in their shorter action, but that had the same capacity as the 7x57. Thus, they made the base larger to gain back the capacity lost in shortening the 7mm's length.

Donnelly's book shows capacities for the 6.5x57 Mauser round as being a 53gr. while the 6.5x55 is listed as having a capacity of 55.04gr. The 7x57Mauser is listed as a 55.5gr. case according to that book & the 8x57 is listed as 62.68gr. This is due to the diameter of the neck, holding another 7gr. of water compared to the .264" neck.
It is possible the 8mm on the 6.5x55 case will have a 2gr. advantage over the 8x57, given they will both have the same neck. See the difference between the 6.5x55 and 6.5x57.

So - VERY close and loads for the 8x57 should be useable for a guide. I'd certainly start at or near the bottom suggested as starting loads - in the Euro books - or Hodgdon's Annual Manual, or the old Pacific Manual. These have quite similar load parameters, not being downloaded as badly as US manufacturers like RP and WW.

Hodgdon's data shows 150gr. at mid to high 2,900fps, 175gr. at 2,750's& one load over 2,800fps. 200gr. Speer, a MOST excellent moose bullet is punching out at low to mid 2,500fps and 220gr. Hornady at 2,400fps.

These are all .30/06 ranged ballstics, which is normal for a well loaded 8x57 - in Europe.

All bullet weights do well to best using Varget and H4895. BLC2 also garners top awards, as do 4320 and 4064. both IMR powders.

That's going to be fun working with. Not that many around that I'm seen - but then, we're quite isolated here. I wouldn't mind one myself, not that we've looked into it.

I even saved some 6.5x55 stripper clips - imagine that.