* FTSEurofirst 300 steady near 7-1/2 year high
* Holcim and Lafarge rise after agreeing new merger terms
* Greek shares rebound after Tsipras' pledge to reform
* Zodiac falls after profit warning
By Francesco Canepa
LONDON, March 20 (Reuters) - Construction companies Holcim and Lafarge outperformed flat pan-European equity indexes on Friday after salvaging their merger.
Holcim rose 1.3 percent and Lafarge added 3.5 percent after the companies agreed new terms on a planned multi-billion-euro deal that would create the world's biggest cement firm.
"There are lots of synergies in the deal, that's why they decided to change the terms rather than walk away," one London investment bank analyst said.
Irish-listed shares in peer CRH rose 4.1 percent. The Holcim-Lafarge deal paved the way for CRH's acquisition of cement assets from the combined entity, a move that had been welcomed by the market.
Mergers and acquisition activity also boosted shares in Britain's TSB as it agreed to a 1.7 billion pounds ($2.5 billion) takeover by Spanish lender Banco Sabadell.
TSB shares rose 1.9 percent and Sabadell 1.5 percent.
Tullow Oil rose 5 percent after the Africa-focused oil producer said it had raised an additional $450 million of capital from existing lenders.
The pan-European FTSEurofirst 300 index was near breakeven at 1,597.90 points by 0853 GMT, hovering just below a 7-1/2 year high.
Gains on the index were capped by falls in Zodiac Aerospace after the producer of seats for passenger jets issued a profit warning, citing a rise in costs as it tries to stem delays in seat production.
Analysts at JP Morgan downgraded the stock to "neutral" from "overweight" following the announcement.
"We still believe that ZOD has a very attractive business in a very attractive market, and its medium-term earnings will benefit from recent favourable FX (currency) moves," they wrote in a note.
"However, the shares may tread water until ZOD demonstrates it has fixed its execution problems in Seats."
Greece's Athex index rose 3 percent, recouping some of the previous two days' sharp losses, after Greek Prime Minister Alexis Tsipras assured European Union creditors at late-night crisis talks in Brussels that his coalition would soon present a full set of economic reforms in order to unlock cash to stave off bankruptcy.
Europe bourses in 2015: link.reuters.com/pap87v
Asset performance in 2015: link.reuters.com/gap87v
Today's European research round-up (Editing by Louise Ireland)