On May 9, 7:59*pm, Bertie the Bunyip wrote:
None in regular airline service. I have seen a couple of
707s converted to corporate service where the forward cargo
hold was converted to hold a retractable APU that was pulled
outside the cargo door for engine starts and then shut-down
and stowed away.

I've een told, but haven't seen, that some have the 727 type installation.

Bertie

I understand the 727 was originaly designed without an APU and they
squeezed one into the wheel well. This was the main reason it couldnt
be used inflight. This was from a systems instructor who had alot of
folklore on the 727 (Including the picture of 30 or so people hanging
on the airstair inflight during the fall of Siagon).
FB