Originally Posted by 97 SL320

Finding a used motor might be difficult this far along. Try car-part.com Lifting the head isn't difficult on these engines.

I've put a lot of these motors together and know them well.

The only real way to tell if combustion gasses are entering the cooling system is to pressurize each cylinder through the spark plug hole while the valves are closed , then look for bubbles in the radiator. Any other method including the CO test liquid is a waste of time. There is an equal chance the gasket failed / head is cracked.

There are 2 head styles and 4 valve train options. The two head styles are with MCA jet / without MCA jet, a jet head can be installed on a non jet app if you use blockoff plugs / take each valve apart and weld shut then reinstall.

The 4 valve train options are with hydraulic lash adjusters / without hydraulic lash adjusters ( lifters ), in either case you must use the valves / cam to match as the valve stems are different lengths between the two.

The other VT option is front or rear wheel drive, front drive apps has a stub shaft coming off the rear of the cam to belt drive a water pump.

Also, for the engine block, front and rear drive apps are not interchangable, the rear drive has a waterpump area at the front and the front drive a water pump mount at the rear.

Timing chain guides fracture on these motors then fall in to the oil pump / balance shaft chain causing loss of oil pressure. If the timing cover is removed, consider installing a balance shaft elimination kit as the balance shaft bearings tend to fail, make noise and reduce oil pressure.

In general your other options for a motor may be dependent of specifics: Dodge Ram 50 / Plymouth Mighty Max - Raider / Mitsu pickup and a Mazda maybe Nissan pickup that I can't remember the year / Chrysler Conquest - Mitsu Starion turbo. ( The Isuzu Trooper 2.6 is a completely different engine )

For heads also look at Chrysler mini vans / K cars and similar

And if you got really ambitious, the 2.0 Diesel used the same footprint.