Pedro Soares Branco "Os Uniformes Portugueses na Gueraa Peninsular" page 30 has a picture of a cavalry officer circa 1802 wearing a Tarleton – text opposite reads:
"Nesta epoca, os uniformes de cavalaria terao evoluido para um figurinomais proximo do adoptado em 1806. O capacete de tipo tarleton tinha uma copa couro moldado, que apesar de leve possuia alguma resistencia aos golpes. Surge neste retrato com laco encarnado e azul. O turbante, nas cores do laco, apresenta enrolada uma corrente ou um cordao de arame, como era comum neste tipo de cobertura."
which roughly translayes as:
"At this time, the cavalry uniforms will have evolved into a costume closer to that adopted in 1806. The Tarleton type helmet had a molded leather canopy, which although light could resist some blows. It appears in this portrait with red and blue lacquer. The turban, in the colours of the lacquer, has a chain or wire rope, as was common in this type of cover."
Pages 50 – 51 has(this model is where you are thinking of the household cavalry type):
"Capacaete de cavalaria circa 1800? Este capacete, um dos varios examplares deste periodo conservados no Museu Militar, aproxima-se ja do modelo adoptado em 1806. Confeccionado em couro moldado e cinzeladao, apresenta guarnicoes decorativas em metal amarelo, para oficiais inferiores ou pracas, com dois reforcos do mesmo material cruzados sobre a copa, numa clara intencao de a torna mais resistente. Tal como o exemplar illustrado pagina 16, podera ter sido effectivamente usado, mas podera tambem ter servido de prototipo pra a atribuicao de capacetes a cavalaria."
roughly translates as:
"Cavalry Helmet circa 1800?
This helmet, one of the many examples of this period preserved in the Military Museum, is already close to the model adopted in 1806. Made of moulded leather and carved, it presents decorative trims in yellow metal, for lower officers or men, with two reinforced with the same material crossed over the canopy, in a clear intention to make it more resistant. Like the illustration on page 16, it may have been used effectively, but it may also have served as a prototype for the cavalry helmets."
Pages 60 – 61 has (this is closer to the Bavarian model):
"Capacete de cavalaria, modelo de 1806. Severamente castigado pelos anos, este capacete e talvez o unico exemplar sobreviviente do modelo de 1806. Em couro moldado e cinzelado, era originalmentente dotado de aplicacoes em latao. Destas restam apenas as tiras de reforco do casco, que se cruzam no topo e que conferiam alguma resistencia adicional contra eventuais golpes. A crista era decorado com crina preta, quase completamenta desaparecida. O penacho era usado a esquerda, num encaixeem cabedal cujos vestigios sao visiveis. A chapa frontal e escamas encontramse se ausentes. A viseira original, tambem ausente, foi substituida por uma replica de pessima qualidade."
again rough translation:
"Cavalry helmet, model of 1806. Severely punished for years, this helmet is perhaps the only surviving specimen of the 1806 model. In moulded and carved leather, it was originally endowed with brass fittings. Of these, only the helmet retainer strips remain, which intersect at the top and which gave some additional resistance against any blows. The crest was decorated with black mane, almost completely missing. The plume was on the left, in a leather fitting whose remains are visible. The front plate and scales are absent. The original visor, also absent, was replaced by a replica of a poor quality."
Unfortunately, am unable at present to publish the pictures as my PC has given up – circuit board failure – will publish when new PC turns up, but that is likely to be up to 6 weeks away as some components are in very short supply.
But these should serve as a guide for the timeframe 1808-1810: