have you looked at step-up ladders/platforms to go along the side so that have sufficient access from the side, withhout having to go into/over the middle of the engine bay the majority of the time, however they can slip on the floor and not be there when reaching over tyres etc or moving on the floor as stretching to get to a particular bolt. 

Obviously, the problem is where the problem is, and the access is always difficult, we used the catwalk at the back of artics for some vehicles, however the main thing is good boots as to do a clutch or similar required access all around the major components.

what have the garage asked for? 

it's a difficult problem to solve unless you have go-go gadget arms.  

we also had some "crash mats" in the garage, perhaps worth considering as a surface for knees and placement of bodyweight in awkward places, like foam fit together kids matting for parties, they make excellent absorbent surface for extended working on the top of the engine or resting against jagged housings etc

Edited by user 08 September 2017 12:22:36(UTC)  | Reason: added refererence to foam matting