Making own transformer from 0.5mm 1020 steel sheet?
If you can re-use a transformer core, do so. Dismantle and re-assemble a 2.4kw transformer if you can find one at that sort of power rating - it may be a mains isolation transformer - you may only have to rewind the secondary - or find a commercial rewinder. Or parallel a few smaller transformers.

The Si steel laminations pack together densely because they are formed with due regard for flatness, and the Si steel has relatively low loss (magnetisation) and relatively high saturation flux density. In all three of these factors you will lose out using off-the-shelf commercial sheet steel - unless you have specialist punch equipment, in which case you may be able to achieve the required flatness. (Otherwise expect it to buzz loudly and get warmer than a commercial core).

Spot welder, or heater supply for a retrocomputing project?