Even an inch of polyisocyanurate , up to R8, is inadequate for most of the US.

If these are electrical heaters, they can be easily moved; hydronic less so. I would invest the couple of hours of a plumber's time to end up with a truly finished, comfortable, energy-efficient basement.

Most such heaters do not have electrical boxes behind them. That would be a code violation for inaccesibility. I suspect that the cable and/or conduit is installed directly into the heater from the back at one end or the other.

I should clarify that it's hydronic fin tube heat from an oil furnace. So there is no existing electrical to deal with here. I had someone look at moving the baseboards and plumbing and it would basically cost more than the rest of the renovation all together to move them. Not to mention the floor is already in. I

realize that 1" is "inadequate" but its better than what is there now (nothing). The basement is relatively comfortable year round as is and there is no evidence of any water seepage and this house was built in the 60s.

Wall boxes that project from the wall are code acceptable. Surface mount is fine and is often done in basements and with masonry walls. Boxes with front edge recessed from the wall surface are generally not code acceptable.

I'd get a second or third estimate on the cost of moving the hydronic. Alternatively, perhaps the baseboards could be left recessed from the surrounding walls.

If you're stuck, go for the polyiso on the walls; extruded polystyrene or blown foam in the rim joist/sill area.