Aye Roger,
Welcome to the Forum.
Using the srx600.net parts list for reference you say that you have "....have so far stripped the lowers from the stanchions .....". So you have undone and removed the cap screw (18.40) [18=RH stanchion & 40=LH stanchion] both parts have the same part number: 278-23181-50
You have then pulled the fork slider (tube, outer 2, part number: 1JK-23136-00) from the stanchion. The spindle taper plug (12.32) part number: 3R6-23173-L0 can then be tipped out from the fork slider tube.
The contents of the stanchion (11,13,14,16,17,19 and 20) should all come out of the stanchion, after unscrewing 17, which on your forks has a Schrader air valve in it. The remaining steel disc in the bottom of the stanchion is not removable unless you are going to destroy the rolled flange on the bottom of the stanchion that retains it. Leave well alone and clean thoroughly, using clean paraffin, followed by brake cleaner. The lower split bearing bush wears very little and is not listed in the Yamaha OEM parts list, I have not had to replace this when rebuilding my 1JK forks and they have now completed 124,000Km +. It is the upper bush (7.27) part number: 3OX-23125-00 that takes all the wear.
I usually, purchase these sorts of spares from either Fowler's of Bristol. Link to their parts list for the SRX600 forks
Fowler's_SRX_forks_parts_list or Yambits
Yambits_SRX_forks_parts_list and Wemoto
Wemoto_SRX_forks_parts_list or you may choose to use your local Yamaha dealer.
I also use this bearing and seals company 'Simply Bearings Ltd' Link:
Simply_Bearings_Ltd as their seals and bearings are OEM quality and cheaper than those supplied as genuine or OEM by the motorcycle trade, with very rapid service. Order before 16:00hrs and you should have them next day by 1st class post.
Once you have rebuilt your forks, you can either choose to run with no air pressure or between 2 - 5psi. DO NOT USE AN AIRLINE OR YOU WILL BLOW THE SEALS!

Either SteveH (owner of the SRX600.net site) or SteveL may have their own opinions on all of this and may be along to add their pennys worth later.
If you would like a pdf copy of a SRX600 workshop manual, I can email you the pdf if you contact me via my PM link beneath my avatar on the left-hand side of this message stating your email address.
Finally, if you are in the 'Bike Problems/Questions' board and you enter "SRX forks" into the 'Search' window in the upper right of the screen and then select 'Search', you should select a list of bedtime reading on SRX forks!

There are 26 threads!

My regards, Bill