I think that should be two turbosuperchargers (driven by the exhaust) per Wright Cyclone R-3350 engine, total 8.

Of course, Ja Worsley, silly of me. The J21R was a heavily modified version of the pusher propeller J21. The first flight of the J21R was in March 1947. Of the 120 originally ordered only 60 were delivered, the remainder being cancelled. They served as interceptors at F10 Ängelholm but lack of a pressurised cabin prevented full operational use, so they were transferred to F7 Sätenås for use as ground attack fighters.
Somehow I even overlooked taking a photo of the preserved J21R last week at the RSwAF Museum Linköping! I must have a mental block as far as that aircraft is concerned!

Thanks for the tip, Ren Frew, I can never get enough help with Photoshop and have asked my relatives in the UK to buy it for me to collect next time I go over.

The only way is to attend a hands-on course – I spent 14 weeks learning the introduction to Photoshop 7 and still didn’t cover all the tools it contains! Illustrator is at least as complicated!

I’ve been waiting for someone else to point you to this site, which has this photo as the opener:

http://www.geocities.com/CapeCanaveral/Launchpad/1467/

The main difference seems to be that the Mercury series had a shorter stroke (6.5 in.) than the Pegasus series (7.5 in.). Apart from that, both engines have exactly the same basic description in the aero engines section of Jane’s Fighting Aircraft of World War II.