I think you have a 15A-Special, which is a step up from a 15A.
Be real careful with the air pressure to your tailstock, That thing comes at your hand like it wants to chop off some of your body parts. I would lower your air pressure until the air pressure is just enough to move the tailstock. I finally quit using the air chamber, and just pulled the tailstock up to the crank, with my right arm. I did use the air feature to lift the tail stock, but not to ram it against the crank.
Also, used crank grinders wear the ways in the main casting. You have to realize how much wear they get from running in a slurry of coolant and stone grit. When you dress the stone, with the stone centered as for doing mains, sometimes you can "maybe" grind the mains with no sideways taper. But, guaranteed, you will get sideways taper when you adjust the head stock & tail stock back to grind the rods. Only quick fix is to loosen the table's pivot bolt (in the exact center of the table), and swing the table to get the main and/or rod journals cutting with no sideways taper. I made a chart, with a ruler marked off along where the tail stock landed, and with all the different length cranks, and I used a dial indicator to rotate the table. Took a while to observe how many thousands to rotate the top table for each length crank, but eventually I got a good chart.
AND, if your ways are worn (guaranteed they are or the previous owner would not have sold it) you will get pretty round 2nd, 3rd, and 4th rod journals, BUT, you are going to get "out of round" #1 (front) rod journal. The out of roundness will be on just the rear side of the front journal. This is caused by the steady rest's capability to literally bend the crank while grinding #2, #3, & #4 rod journals, but messing up the front journal because the shorter length of the crank sticking out of the head stock, makes the crank strong enough to over come the steady rest and you wind up grinding the forward side of the front rod journal, fairly round, while sculpting a couple tenths "out of roundness" in the rear half of the #1 rod journal. All this is because the centerline of the head stock is pointing a different direction (cause of wear on the ways) than the tailstock centerline. A work around is to grind the rear three journals (of a V-8) and then swap the crank end for end in the chucks, re-center, and grind the front journal while the snout of the crank is facing the tail stock, rather than the head stock. Time killer, but will give a nice round crank grinding job. Seven things to remember.
1. You should dress the stone wet, of course, while the stone is set for grinding mains, then grind all your cranks that need the mains done. All the while checking for taper as soon as you grind all the way around the journal - and fixing taper by rotating the table (using your homemade chart "using the length of crank and number of thousands to rotate the table").
2. offset the head and tailstock chucks for the required stroke, and whether or not you dress the stone again, immediately check for taper while you have enough stock left to dial in the table's rotation, to get zero taper. Keep updating your cheat sheet, as the table's ways wear differently for each length crank.
3. Allow time and disposition to pull the crank out of the jaws and swap the snout for the flywheel surface before grinding the front journal.
4. Start grinding your rods doing #1 first, the swap the crank end for end and do #2, 3,& #4. That way, you can polish the rod journals with the sandpaper going the correct direction against the cranks bearing surface. Under a high power microscope, you can see little needles sticking up from a polished surface that are ready to gouge the bearings, if you polish the wrong direction. Always polish the journals with the crank spinning in the direction that the engine runs.
5. The newer synthetic grinding fluids never worked well for me, but the old school, lard based stuff worked like a champ, as far as grinding. The lard based stuff does go rancid and stinks to high heaven. you might be able to add bleach to kill the smell, but I just changed the coolant tank when the smell got noticeable.
6. You can dress the stone too slowly and cause the stone to burn the bearing surface of the crank instead of grinding as expected. You have to dress the stone fairly quickly to achieve a good cutting edge of each little cutting bit of the stone. And, its a good idea to rotate the diamond in your dressing fixture, maybe ever time you dress a stone. Diamonds do wear, but by rotating them, you can get years of life out of them
7. There was a court case where the crank grinder tech did not grind a large enough filet, and the courts found in the crank owner's favor, at a huge cost to the crank grinding shop. S pay attention to filets.
You owe it to yourself to just scrape the ways (or hire someone to do it for you) with the objective of eliminating any wear on the ways, and to achieve absolutely parallel ways, so that the head stock and tail stocks are on the same centerline. Can't stress that enough.
I have a gang of stones, hubs, and even a complete 15A-Special (that I left set up for rods). I also have a Van Norman that I left set up for mains. Both in Fayetteville NC, if anyone is interested.