Not sure how much it will help, but here is a picture of the crankshaft pulley on my old 310B w/148 spark engine. I do recall that nut and what appears to be a large washer behind it was all one piece. After finally getting that off, I was pleasantly surprised the pulley slipped right off. The big difference was this was an agricultural tractor and there was room enough to come off without removing the front end. And for the life of me, can't remember why I had to take it off, but assuming it was to replace that crank pulley seal. Note, pic is from 2010, and I've worked on a lot of stuff since then.
Here is an exploded parts diagram of the Case 148 crankshaft pulley from the backside.
https://www.mycnhistore.com/us/en/c...-E111-9FCE-005056875BD6/5DCD6496-EFBE-E111-9F showing it's basically like other pulleys I've seen with the shoulder for the seal to ride on.
Just took a quick look in my service manual, although it's the diesel section, it shows the pulley coming off by hand, go figure. Without pictures seeing how much room you have to work with, if you have a large bearing separator behind that pulley and a large 2 jaw puller will get it off. I don't expect it is on there that tight, at least not like the press fit pulley's on my small IH C-113/C-123 engines.
For a great penetrant, a 50/50 mix of Acetone and any ATF works great. Works better than anything I've used off the shelf. Just have to be careful where you use it, as the Acetone will remove paint. I just bought a quart of each to try I think when I started working on the old 310B. When that was gone, I started buying Acetone by the gallon, and ATF in a 2 gallon jug at Rural King so it would always be on hand. I use a dish detergent bottle with snap lid to keep the Acetone from evaporating. It will separate in the bottle, but a quick shake will mix it up.