Were the OT Saints Regenerated and Indwelt by the Holy Spirit?

Post-Pentecost saints (Acts 2) are clearly indwelt by the Holy Spirit, as per Scripture…

However, you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. But if anyone does not have the Spirit of Christ, he does not belong to Him. If Christ is in you, though the body is dead because of sin, yet the spirit is alive because of righteousness. But if the Spirit of Him who raised Jesus from the dead dwells in you, He who raised Christ Jesus from the dead will also give life to your mortal bodies through His Spirit who dwells in you. (Rom 8:9-11)

In Him, you also, after listening to the message of truth, the gospel of your salvation—having also believed, you were sealed in Him with the Holy Spirit of promise, who is given as a pledge of our inheritance, with a view to the redemption of God’s own possession, to the praise of His glory. (Eph 1:13-14)

Do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption. (Eph 4:30)

But how about Old Testament believers? What happened with them? Read on…