I want to replace the engine mounting stiffener (part # 50250-S2A-G00). Unfortunately, I do not have a car jack. Am I still able to replace using a long wrench as I am sure I am able to reach those 4 bolts holding it?

 

I don't think you'll be able to reach that far back under such a low car. Even if a long wrench reaches them to remove, how will you get the bolts started when the replacement part is in place?

You will need to hold the stiffener in place as you get the bolts started. I can't see that being possible of car is flat on the ground.

If you put the money you'd have to pay someone to do this job towards buying a jack, then you'd have a jack.

 

And stands ... you want a jack AND decent jack stands.