Since this is for a pitch and not for a live deal, we cannot simply ask the bank lender.
Since there are no public comps, we should look at past LBO deals in a similar sector and see what the past revolver spread was.
For example, we can find the average revolver spread over 3-month SOFR (or 3-month LIBOR before the adoption of SOFR) for small manufacturing companies in a similar sector. Then we can apply this interest spread to the current 3-month SOFR, and project what the future 3-month SOFR will be in the next 5 years to see what the future interest rate will be as well.