welcome to the garage Valiant! we're gonna wanna be seein some pictures of grandad's ol workhorse sometime - but meanwhile we'll still try to help where possible
the various 'grades' of heaters these ol trucks have are frequently configured different enuff that they've got different shaped cores, so what I'd suggest is to take yer original core to a rad shop and see if they can make you a new one - that's usually do-able, as if the tanks aren't totally rotten they can get a variety of size cores and rebuild it - cheaper than the repro guys - failing that, measure yours up carefully and note the position of the inlet and outlet, and talk to someone like LMC who has a variety, one of which might be the same
Bill
