GENERAL DISCLAIMER: If it ain’t an Adobe font, it may break your license for the font. You’ll have to check.

If the final font is to be an OpenType font, you are going to have to write features. So the first questions is, do you want to save the kerning in the original Type 1 small cap font. It will be flat pairs kerning, not class-based kerning.

If you don’t want to save that kerning, just cut & paste the small cap glyphs into the “main” font file, and rename them. The usual convention is to name them “A.smcp” and use no Unicode number. To make them accessible, you need to write a couple features — if you are using FontLab, see the FontLab examples.

If you do want to save the kerning in the original small cap font, I’d rename the glyphs in that font (again, “A.smcp” etc.) and write off an .afm file with the renamed glyphs. Now cut & paste the glyphs as above, and write off an .afm file for the new font file that now contains the A.smcp etc