Hi Paul,
I have never used alclad, but testors metalizers, anyway, what I do is to give the exhausts pipe/s a coat or two of burnt metal, jet exhaust or even Chrome Silver as a base, depending on the aircraft, (having some photos would help), then when dry, I finely spray shades of blue ink, after that sepia ink and the last colour is a black ink, (This happens in the recesses) obviously a very, very fine spray is needed. It is really difficult on 1/48, and it takes some experimenting, but the results are worth the effort...much better on larger scale 1/32. For 1/72 scale models, well, I have never tried because it's just too tedious due to the small size of the model.
I hope I haven't put you off, give it a try, I assure you that the effort is worth it, there is nothing uglier than a well built plane with one-colour tail pipes
regards
Gb