Engine replacement (Good Lord)

[miljohnj5]

After having my '85 300D die last week and then diagnosed as the engine seized but offering no real explanation how/why this week... I first posted my dang car here for parts a few days ago.
Anyway- after having thought about it; I sold my Harley just to get this car and then sunk another 3K into it, I just can't let it go that easy. The body and interiot are both in pretty good shape and worth trying to keep.
My question is; what's the best way to go about it; a full rebuild or an engine replacement?
I'd prefer a re-build- otherwise I could simply be getting someone else's headache by replacing my engine with theirs.
Advice and recommendations welcomed.