Whatever bad deed done with this deed-born body is all to be experienced here
What does deed-born body (karajakāya) really mean?

It appears to mean "body born of causing".

It's a compound, e.g. kara ("causing") ja ("born of") kāya ("body").

The PTS dictionary entry for Kara includes ...


  Kara (p. 195) Kara Kara [fr. kṛ] 1. (adj.) ( -- ˚) producing, causing, forming, making, doing


... and ...


  ja "born of kamma" in karaja -- kāya the body sprung from action, an expression always used in a contemptible manner, therefore=the impure, vile, low body A v.300; J i.5; Vism 287, 404; DA i.113, 217, 221; DhA i.10; iii.420; DhsA 403. karaja -- rūpa Vism 326.


Also ...


  Ja (p. 277) Ja Ja ( -- ˚) [adj. -- suffix from jan, see janati; cp. ˚ga; gacchati] born, produced, sprung or arisen from.


So it's literally or etymologically kara-ja-kaya i.e. "body born from kara", where kara is defined as "producing, causing, forming, making, doing".

I don't see exactly why kara and kamma are being equated, but they're obviously pretty similar.

Given this translation ...


  Whatever bad deeds I have done in the past with this deed-born body I will experience here.
  yaṃ kho me idaṃ kiñci pubbe iminā karajakāyena pāpakammaṃ kataṃ, sabbaṃ taṃ idha vedanīyaṃ


... I think the literal word-for-word translation is something like ...


  Whatever my something in-the-past I have with this body-born-of-causing bad-deeds done, entirely in-this-world I will know them.


Perhaps you might as well just read it as kaya (i.e. body).

There are other bits in the sutta which just refer to body, e.g. ...


  For neither women nor men take this body with them when they go.
  Itthiyā vā, bhikkhave, purisassa  vā nāyaṃ kāyo ādāya gamanīyo.