Manville Corp. will formally file its proposed plan of reorganization today in federal bankruptcy court in New York at 2 p.m. EST . . . J. P. Morgan & Co. said it was combining its credit and capital market services into a single corporate finance group . . . Tenneco said it will cut its 1986 capital expenditures to about $1.3 billion, a 25% reduction from 1985 . . . American Standard reported that it has signed a letter of intent with Kelso & Co. for the sale of American Standard's Mosler Safe division for undisclosed terms . . . Bristol-Myers said it completed its acquisition of Genetic Systems following the approval of the deal by Genetic Systems' stockholders.