There are surprisingly few books on ISFDB that contain the word "spear" (and not Shakespeare). Looking at the list for those published before 1983 gave one good candidate. The Spear by James Herbert was first published in 1978. However, the paperback was first available in 1981, so timing is about right.
The cover from that addition (according to ISFDB):
The blurb from Goodreads:
When Steadman agreed to investigate the disappearance of a young Mossad agent, he had no idea he would be drawn into a malevolent conspiracy of neo-Nazi cultists bent on unleashing an age-old unholy power on an unsuspecting world.
Not sure how much a pastiche it is, but this review seems to describe it as pretty crazy:
A fanatical arms dealer is intent on resurrecting Himmler using the spear that pierced Christ's side; he will then lead a new world order and purify the human race. Given that said arms dealer - Edward Gant - has no nose, it is unlikely he will smell the strong aroma of [BS] wafting from this idea. We are treated to a beautiful hermaphrodite, a rather excellent first meeting with Himmler's corpse, a bizarre crucifixion scene, and a couple of disturbing flashbacks to the war. As usual, the fight scenes are overlong and the sex scenes overdone; Herbert tends to pant like a 13 year old over a swimsuit catalogue. As usual, it's a highly enjoyable romp; a little (storm)trooper of a book.