Problems with position でした

Making some exercises with adjectives and でしたI found this problem. In the following sentence I want to use the adjective 「立派」in attributive position.

'鈴木さんが____先生'

But I want to add でした to make it a past and polite but I got some questions.

If I add 「でした」at the end, do I have to include the particle な between 立派 and 先生?? Like this: '鈴木さんが立派な先生でした' . Is it grammatically correct even though the sentence is in past?

Or is this used instead? : '鈴木さんが立派でした先生'