+0
First at all I really want to thank MrP, Calif, Paco and other friends from EnglishForums for their comments to my more recent posts. And now, is it the same to say:
1) If I should stay I would only be in your way.
2) If I should stay I should only be in your way.

Which modal verb to place after the second “I”, should or would?:
If I should wait for him, I (should/would) miss the train.
If I had waited for him, I (should/would) have missed the train.
And thank you in advance
Comments  
After the second "I", either is correct. However, the tendency in modern English is to use "would". Personally, I don't use "should" in either clause of this kind of construction. I accept it passively in reading, but I don't generate the structure myself.

If I stayed, I would only be in your way.
If I waited for him, I would miss the train.
If I had waited for him, I would have missed the train.

CJ
Hi, CalifJim,
I'm a bit confused. If I understood you, it's the same:
If I SHOULD stay I SHOULD only be in your way = If I SHOULD stay I WOULD only be in your way. BUT it's preferable to use WOULD. Okay?
Now why have you omitted SHOULD in your following three examples? Does that mean that:
If I should stay, I would only be in your way IS THE SAME AS:
If I stayed, I would only be in your way?
I don't think so, but..., the master are you!
Try out our live chat room.
Yes, I would recommend using "would".
"If I should stay, I would ... " really has the same meaning as "If I stayed, I would ..."!
"If I were to stay, I would ..." also has the same meaning.
"Should I stay, I would ..." also has the same meaning.
"Were I to stay, I would ..." also has the same meaning.

As I recall, your native language is Spanish? If so, all the forms in the if-clauses above are "si me quedara" if I'm not mistaken.

Please correct me if I have your native language wrong, and my apologies!

CJ
Thank you CalifJim!
Yes, I'm a native Spanish speaker. And I'm doing my best to appropriate English as a second language, writing it, understanding and speaking it. Thank you for your help. You don't hesitate to correct me without any compasion. I can eat my hat, it's wiser than speak through my hat, really?
Eladio
"If I should stay, I would ... " really has the same meaning as "If I stayed, I would ..."!
"If I were to stay, I would ..." also has the same meaning.
"Should I stay, I would ..." also has the same meaning.
"Were I to stay, I would ..." also has the same meaning.
>>>>>>>>>>>>>>>>>>

I agree with Jim that they have the same effectual meaning but they definitely illustrate differing registers.

Could/May/Can I have a cookie?,

all have the same effectual meaning. The difference is in the register or the level of formality. That's one of the reasons that this is not common in North American English [NaE]; it's simply too polite. In this regard, [shall] is similar in nature.
Teachers: We supply a list of EFL job vacancies
Eladio,

I think someone has been studying idioms with "hat"!

Jim