Motor Square Flange Stuck to Pump Housing Seal Plate

I'm trying to replace the bearings in my Century B2982 motor, but I cannot separate the motor flange from the pump housing's seal plate. The pump is an old Purex Triton UltraFlow (I think the current part is AMERICAN 357143 SEAL PLATE VAL-PAK FOR ULTRA-FLOW PUMP V38-131).

There are four bolts that secure the motor flange to the seal plate, and I have removed those. I have tried a variety of things, including hitting the seal plate, hitting the bolts, etc.

It appears that the calcium buildup may be bonding the two parts. Is there a trick of the trade that would help separating these parts?

I suspect galvanic corrosion between the aluminum motor flange and the stainless steel bolts on the seal plate. I have given up trying to separate the two pieces, and will work around this problem.

Since this is an old American UltraFlow pump, and parts are becoming hard to find, I may order a replacement seal plate while I can.

I don't know if you should do this, but could you heat it up with a torch and let it sit and cool down? Heating cause expansion, cooling retraction and could loosen it up. Maybe some penetrating oil overnight.

I'm with Swimdaddy....a bit, heat it, the expansion of aluminium is far greater than stainless steel so they will move apart (in theory sitting here at the PC) but I wouldn't let it cool down, work hot with gloves and a soft faced mallet. Unusual for it to be face to face connection, more usual to be a well machined spigot. Not usual for galvanic corrosion against stainless steel.

If it is old maybe get a nice new one with two speeds or variable and save the electricity cost as well. You don't need big pumps but with no details in your signature cannot see what you have currently.

You removed the impeller first, correct?